How to fit forks to fixie frame
Park tool has plenty of information on how to do this, including how to cut a fork (and what tools are useful, namely a saw, a vise and a saw guide). They also have other directions, e.g. how to prep a frame for headset installation and what not. 

Depending on the tools you have, and how prepared the frame comes, you may want to leave some of the preparation to a bike shop (e.g. very few home mechanics are equipped to ream/face a frame properly).