AM: you have a carrier wave of a much higher frequency than what you intend to transmit. You vary the amplitude of that carrier wave so that it matches the profile of the wave to be transmitted. Its fairly simple to make such a tranmitter. Recieving it, like receiving anything to do with radiowaves, is witchcraft, and to be avoided at all costs by anyone who values their sanity.

FM:..... yeah. Same kinda thing but you vary the frequency of the carrier instead of the amplitude.