The bottom three get wired to AC house current/mains.
SO i guess I need to take a PC power cord....cut off the end then splice the 3 wires into the bottom 3 slots of the pictured power supply?
If so which cable goes into which? ie- what is the difference between AC1 and 2 and that symbol thingy?
yes
the symbol thingie is what's known as "ground" and gets wired to the green lead inside your cord.
AC1 and AC2 are the white/black wires (alternatively brown and blue depending on where your cord was made) normally the very bottom most lead is the "hot" wire (black or brown) and the next one up is "neutral" (white/blue)
this will result in a power supply that is powered all the while the cord is plugged into the outlet. if you need to switch it off and on, you are going to need to supply some kind of toggle switch.