Voltage can be thought of as the pressure or strength of electric power. All things being equal (see AMPS below), the higher the voltage the better, because high voltages pass more efficiently through wires and motors. Very high voltages (100+ volts) can give you a nasty shock because they also travel through people rather well, but the sort of voltages found on electric bikes (12 – 36 volts) are quite safe. As a rule, a 12 volt system is fine for low-powered motors, but more powerful machines work better with 24 or 36 volts. Electric mopeds and motorcycles tend to use higher voltage – typically 48 or 60 volts.
Amps can be thought of as the volume or quantity of electric power. To aid this analogy, the flow of amps is called the current, as in the flow of a river. Unlike a river, though, the speed of the current is fixed – only the volume varies. The maximum flow of amps in a bike drive system can vary from 10 to 60 or more. A current of 60 amps requires thick wiring and quite substantial switchgear.