There are three main parts:
3) Float sensor
and the last section (4) contains some notes on testing
Don't be intimidated, these are not that hard, but you do need some electronics experience to make it easier. If you feel you can't trust your soldering skills, it might be a good idea to use a chip socket for the 555 chip that we use.
Generally, the design works with the fact that the water reservoir uses a magnet (right side of closeup picture) to sense that it is empty. We will use a reed relay, which can be activated by this magnet, to initiate a fill cycle.
You will need to read through the whole process to be assured you can do all of the steps, and that you have everything you need.
Step 1: Plumbing
-electric valve ( search Ebay for 12V valve 1/4", make sure pressure rated. example http://www.ebay.ca/itm/12V-DC-1-4-Electric-Solenoid-Valve-Air-Water-Diesel-/180784450198?pt=Pneumatic_Hydraulic_Valves_Parts&hash=item2a1797ca96)
-fittings to connect hoses to electric valve (thread to hose adaptation as required), with Teflon fitting tape, or paste.
-high pressure 1/4" (cloudy white color) hose
-1/4" clear hose
-bushings / collars for hose ends
(all items above at home center except electric valve)
By far the most expensive parts in this step are the two valves (shut-off & electric), which are about $10-15 each.
You will need to start by putting in a tap from an existing water line. Make sure you turn off the water and relieve the pressure before installing the valve. I would NOT buy a cheap 'saddle valve' , the kind that pierces the pipe by itself. I went through a couple of these before giving up. They are not worth it, and even illegal in some places because they can leak terribly!
Since the hose between this valve and your electric valve will be under pressure, I would get the (cloudy) 1/4" higher pressure hose and not the clear stuff. After the electric valve, I would use the 1/4" clear hose, as it is easier to work with, and not under pressure. You will need some of this anyway, to insert the level sensor we'll be making later in step 3.
It might be an idea to buy an ice-maker kit (which you would otherwise buy for your fridge), which includes the shut-off valve, hose and some other stuff. I realized this after I bought all the other parts piecemeal.