Marion, Simplistically, amps (amplifiers, not amperes) are electronic devices that process an input signal and pass it through to another device at a higher volume. The input may be from a microphone, instrument pickup, tape deck, etc.

A speaker (actually, loudspeaker) converts the electrical audio signal into sound vibrations in the air so they may be heard by listeners.

A monitor is usually a loudspeaker that points back at a performer instead of out toward the audience so the performer can hear what the audience hears and adjust the volume and balance between performers and instruments accordingly. Monitors may also be used inside a studio control room so the engineer can hear what is being recorded.

Hope this helps,

      - Mark