How to Assemble the SMPS into the Case

4 screws hold the PSU in the case. You will see 4 screw holes in a slightly odd-ball pattern that line up with holes in the PSU.

Build it yourself:
http://www.tomshardware.co.uk/forum/274745-13-step-step-guide-building

Suggestion: if it is a top mount PSU, turn the case upside down and let gravity work for you.

Another suggestion: if you have a bottom mounted PSU and the fan opening is facing up toward the inside of the case, cover the fan opening until you are done building so you do not drop hardware inside the PSU.
 

Wouldn't it be easier ti just lay the case on it's side ;)