First of all "keep your distortion/overdrive in front of your amp" Means plug your guitar to your pedal then your pedal to your amp
Goes like so:
Guitar< ------------>pedal<----------->amp. Required two chords.
When they say put the wah behind your amp it means into teh effects loop.
The send and return is The efects loop were you would plug your effects into.
This works like a series circuit.
Cable goes form the return into the input of the wah pedal (left side of the pedal), then another cable goes from output(right side) of the wah pedal into the return.
Preamp and power amp
Kinda simple. Your guitar signal goes the preamp first. The preamp is what shapes your tone into what sound you like, then the signal goes to the power amp. The poweramp takes your signal and amplifies it making it louder so you can hear it. Then the signal goes into the speaker.
The amp you have the preamp, poweramp, and speaker into one.
So basically it goes:
Guitar<-------->Preamp<--------->poweramp<-------->speaker<---->your ears. Generally
with the effects loop envolved it goes:
Guitar------->Pedal------->preamp------->Send------wah-->return----->poweramp------->Speaker----->your ear pussy.
Heres some posts that helped me learn some stuff about amps
Hope that helps a little.