The only thing you have to know is that you're changing the profile of the bar, but leaving the volume the same. You can beat it out into foil, or forge it into a sphere, but it'll still be the same volume.
Step 1: Upsetting Steel bars
Heat the end of the bar, or the bit you want to be wider to forging heat. Place the bar end-down on the anvil and hit the top, like hammering in a nail. If it cools down too much, put it back in the fire until it gets hot again, then carry on. Upset the bar until it's at the desired thickness.
You can use Upsetting to put bulges into a bar, or to make rivets, nails, bolts, ETC
Step 2: Twisting Steel bars
Step 3: Hot Cutting Steel bars
(the axe was on fire, not long ago)
To cut a bar, bring it to the correct heat, set it on the hot cutter and hit the steel over the hot cutter. Each hit from the hammer pushes the steel down and cuts it a little more. Only cut partway through the steel. If oyu cut all the way through, you'll probably damage your hot cutter and there's a good chance that you'll have a piece of hot steel flying off into some obscure corner and causing trouble. When the steel's almost done, the hot cutter will draw heat out of it quite quickly, so you'll see a darker line on the bar. Grab the steel in pliers and pull it apart.
Step 4: Drawing out steel
As always, don't let it get too cold.
Step 5: Bending and Straightening steel
To straighten steel, heat up the bend, put it on the anvil and hit it with the hammer until it's straight. Chances are, you'll put some smaler bends in as well, sort them out too. It's really as easy as that.
To bend steel, heat the bit you want to bend, put it over the anvil and hit it till it's bent. Again, really, really simple.
Step 6: Making Loops
Get your steel and put a 90 degree bend in it. You'll need to put the bend about 3 or 4 inches in, or more or less, depending on how big you want the loop to be.
Put another 90 degree bend in the steel, facing the other way, so you get a step-like shape. The step-bit needs to be about an inch long.
Bend it again about .75 of an inch up from the step, this starts the loop. By now, you should have a question mark shape.
Heat up the back of the question mark shape and bring the end of the bar around, so it touches.
If needbe, or if you want to, bend it over, or straighten it.
There's more stuff you can do with hot steel, but basically, it's all variants on what you've seen here. Flattening, for example, isn't dissimilar to drawing out.
Thanks for reading.