in the mobo with a 3 pin plug and into the power supply with a 4pin molex
if they came with a 3 pin only, that is for a mobo, if it is 4 pin that goes into a 4 pin like the the dvd has
most fans come with a 3 to 4 pin adapter if they are 3 pin
you can get y lines and spliters too - if you do not have a free 4 you may need a y spliter same with 3 pin
have fun!