Water cooling is pretty simple, if you take your time. To water cool a GPU you need a radiator, a pump, a reservoir, tubing, fittings for each piece, fluid and treatment chemicals, and a water block. You want all the pieces to be the same materials, copper/brass as the base metal. Avoid aluminum parts unless you plan to buy *ALL* aluminum parts.
So first step is research. Figure out what you need and where you can get it. I got all my stuff from EKWB (except for one fitting which i got from XSPC cause I missed it on the first pass) You may want to look at their kits to get an idea of all the parts you'll need for your build. Then you can look at the installation manuals too. Then you'll probably want to draw out a plan. Remember that...