The most general answer is that it uses one or more industry standard serial interfaces. The data to be transferred is broken up into blocks of data called packets. The packets are made up of individual characters or bytes, typically 8 bits in length. The eight bit bytes may go over the wire with either the most significant byte first or the least significant byte first. The crucial thing here is that both ends must agree on the same set of rules, which is often called a protocol. It means the same thing as in diplomacy.