How do you hook up 4 speakers to a 2 channel amp?

Connect wire from the negative terminal of left channel to the negative terminal of the first speaker. Then connect wire from the positive terminal of left channel to the positive terminal of first speaker. In this way corresponding terminals of left channel and first speaker will be connected to each other.

Do all speakers need an amp?

So, the answer is no. Powered speakers dont need an amplifier. The terms powered and active speakers are often used interchangeably, but there is actually a difference between them. In a pair of powered speakers, there is usually only one amplifier that is built into one of the speakers.