These instructions should not be attempted on an actual rock face as there is a difference in procedure between an indoor rock gym and a rock face.
Step 1: Prepare for climbing
First double up both of your webbings (if they are too long), so that it reaches from your harness's belay loop to slightly above your head. Then attach a locking carabiner to one of the webbings and then to the belay loop of your harness. Lock the carabiner. Then use another locking carabiner at the other end of the webbing which will be placed on an accessory loop of the harness for now. Do the same with the other webbing. Hook the ATC to a locking carabiner and place it on an accessory loop, and keep your extra carabiner on an accessory loop. You can also bring an extra ATC with you as a backup if you have it. (I can't tell you how many times I have accidentally dropped equipment when rappelling!)
You can also use extra cords to ensure that you will not drop equipment, however, these can get tangled and in the way very easily.
Step 2: Climb to the top!
It might help to use a carabiner through your crotch strap and belay loop rather than tying yourself in with a figure 8.
Step 3: Tie yourself in
Some top ropes will be wrapped around a "weight bar" at the top of the climbing wall. These bars will have two "holes" on each side of the bar. You will take one of the locking carabiners attached to the webbing off of your accessory loop, and clip it into one side, and the other carabiner from the other webbing into the other side of the weight bar. Make sure to lock your carabiners.
Two quick draws:
Some top ropes will be setup through two quick draw carabiners (Most will have the quick release carabiner replaced with locking carabiners in a permanent setup). You will unclip one of the carabiners attached to the webbing from your accessory loop, and clip that into one of the anchors, and then unclip the other carabiner from your accessory loop and attach that to the other anchor. Make sure to lock your carabiners.
Some climbing walls will have "eye hooks" as you go up the wall. These will hold your weight if you do not want to go all the way to the top, however, it is best to use two at the same time as a redundant backup, so unless there are two already in the wall where you want to rappel from, bring an extra one with you. Clip into these the same as you would the anchors listed above. Make sure to lock your carabiner.
Step 4: Test your connections
Step 5: Preparing to rappel
After both ends of the rope are even on the floor, you will then take the carabiner and the ATC belay device from your accessory loop and attach it to the belay loop of your harness. (You can attach it to the crotch strap and belay loop, but it makes it almost impossible to put the ropes through so I don't recommend it unless you have had some experience working with ropes while attached to them.)
Hold the ATC up so that one "hole" is closest to the wall and the other is closest to you. If you are right handed (or are used to belaying right handed), you will want to make sure that the excess rope is coming out to your right once you hook the rope into the belay device. Reverse that for lefties. You will want to move both ends of the rope to whichever side of your body the excess rope will be coming out, and make sure that both of them are in front of you and one isn't behind you stuck on the webbing. This happens quite frequently. Once you have moved both ends of the rope to whichever side you want them on, squeeze the inside rope through the hole that is closest to the wall on the ATC. Then squeeze the outside rope through the hole that is closest to you on the ATC. You should then have a small loop of rope on the ATC. Clip the carabiner through both loops of rope (and it should already be through the wire holding the ATC).
Step 6: Testing connections again
Step 7: Rappel down
Once you are at the bottom of the wall, you can unhook everything from your harness.
Step 8: Safety concerns
1. Suspension Trauma:
Suspension trauma is a condition that occurs when you have your weight sitting in a harness for too long. The harness will interfere with your blood flow. Your heart will be strong enough to pump blood down into your legs, but not back out; basically you are bleeding to death inside your own body. Your blood is then pooling down in your legs causing your muscles to die, which then in turn releases toxins into your blood. Because all of your blood is pooling in your legs, your brain has reduced blood flow so you will eventually pass out. Most climbing harnesses are rated between 15 and 20 min before suspension trauma will start to set in, but you should check your documentation to be sure of the rating. Always make sure you are on the ground at least 5 min. before the time rating so that you can allow for any unexpected event. Some cheap "safety" harnesses have as little as 4 min. before suspension trauma becomes critical. If you suspect that someone has suspension trauma, or if someone passes out while on a climbing wall, try to keep them standing up and walking around, or at worst, sitting. DO NOT Let Them LIE DOWN! The pooling of the blood can cause clotting, which is why you want them walking around. Call a paramedic immediately, and explain to them as best you can what is happening. Many paramedics (at least in Illinois) have not heard of suspension trauma, but there is another condition called compression syndrome that they will know about, so you can always tell them that the victim has something similar to compression syndrome (an older term is closed cell injury). Suspension Trauma is the number one cause of fatalities in rock climbing.
2. Equipment breakage:
Safety equipment does not last forever, so be sure to check carabiners for signs of wear or problems with their operation, ropes for signs of stress (this needs to be done after every hard fall... many ropes will need to be retired after one hard fall), webbing for signs of stress, knots to be sure they are tied correctly, and your climbing partner to be sure they are hooked up correctly. This should be done before every climb. Also be sure to check your knots before using them.
3. Climber error:
Some times you can make a mistake when connecting your equipment. Always test your connections before using them, especially when switching to a new connection mid-air. If something doesn't seem right (even if it is something that you think wouldn't matter), be sure not to use it, and have your belayer lower you down.
Be sure to come down slowly when you are rappelling - you are not in the movies. As you come down, the friction on the ATC causes extreme heat build up if you come down fast. In some cases, you will not be able to slow down, or it could damage or even burn through the rope. (Not to mention that you can burn yourself.) If you do come down fast by accident, do not slow down or stop, keep going at the speed you are descending at, but do not speed up. Gloves are also very nice for rope work, so that if you start to go fast, you can let the rope slide through your hand without rope burn.
Special thanks to gmoon for reminding me about the following:
5. Clothing and hair:
Be sure that any part of you such as your clothing, hair, etc. can't get caught in the belay device. If at all possible, take everything that you don't need off before climbing (jacket, extra straps, etc.). Also, you should never wear jewelry when climbing. Necklaces and dangly earrings can get caught in ropes, rocks, equipment, etc, so never wear them. Tight watches on the opposite side of your belay hand are fine, as well as studs in your ears, but nothing more than studs or watches.
6. Equipment lockup:
Never lock the carabiner once it is holding any weight. You will damage it, and it will not want to unlock. If this happens, put weight on it when you are trying to unlock it, and sometimes it will unlock easier. If it does lock up, retire the carabiner immediately.
7. Check your connections:
As I said in steps 4 and 6, always put your weight on your webbings and rappel setup before unhooking from your rope and webbings.
8. Hard falls (AKA "Shock weighting):
NEVER stress your equipment by "jumping" on it, or by falling on it when there is any slack in it. This is especially true with any type of static line. Webbings, and assault rope are both static lines. Should you have any slack in a static line and fall, retire it immediately.
Step 9: Fireman's belay
A good practice (especially on your first few rappels) would be to have a buddy/belayer use a "fireman's belay" at the bottom. Basically what they will do is hold the rope loosely as you are coming down, and should something happen to you (you pass out, freak out, get knocked out, etc.), they will pull straight down, (taking out all the slack between them and the ATC), which will break for you until you can regain control. If you are incapacitated and they are experienced, they can also adjust the angle at which the rope is held, slowly letting you down, which makes this method superior to other backup methods because your buddy/belayer can let you down, rather than having you stuck there dieing from suspension trauma.
Step 10: Conclusion
Special thanks to Gmoon for helping me on this article.