Ditto only knows the move Transform, which turns Ditto into the opposing Pokemon, copying type, appearance, moves, and stats - besides HP. Any moves copied are set at 5PP. Ditto can be found by using the Cloning Machine with a random chance instead of Mewtwo. It can also spawn naturally, but extremely rarely.
Because of the way it can transform into any other Pokemon, it can breed with any Pokemon. Ditto is highly sought after for this reason.