the small 2pin or 3pin plugs are meant to be plugged directly into your motherboard. normally a board has at least 4 such ports. this allows your computer to automatically control the fan speeds without any direct interaction from you. i believe you can set this up in bios but i know you can also control them through software such as speedfan.
if you want to connect them to your psu directly they will be always on, probably at 100%. 80mm fans arent as quiet as 120mm so you might want to see if they are too loud for your liking. there are molex to 2/3pin fan connector adapters available. you should be able to pick up a whole pack of them for pretty cheap.
if they make too much noise there are front plate fan controls available. there are also internally mounted fan controls available.
for a new pc builder i would suggest just keeping it plugged into the motherboard.