If you have some old electronics in your house that you plan to throw out, use the power adapter for it.
Look at the back of the adapter for output voltage. It really doesn't matter the output voltage, the higher, the faster your fan will go.
Splice and strip the end of the wire. Depending how you connect your wires determines in what direction your fan spins and how you mounted it will also depend if it is an intake or exhaust.
Don't stress out, it may seem complicated but once you get the hang of it, its pretty simple