The common 13 amps switch sockets that we use in our house is made up of a very simple and direct circuit consisting of only three wires, the Live Wire, the Neutral Wire and the Earth Wire. The fact that we might see more than 3 wire terminals when we remove some sockets is simple because the extra wires runs to another switch socket nearby. It is within regulation and safety standard to have 2 switch sockets sharing the same circuit and the same circuit breaker.
Looking at the circuit diagram above, three wires, namely the Live, Neutral and Earth comes from the mains and are depicted by their respective color codes. The 3 wires goes to the first switch socket which, in normal cases will be the one that is nearest to the mains. From that switch socket, another 3 wires are run to the adjacent one making a series. When terminating first switch socket, the wires with the same colors are twisted together before termination.
All 13 Amps switch sockets are designed for use in electrical apparatus that does not exceed 13 amps in current consumption. Anything that consumes higher than that should not be plugged into a 13 Amp switch socket. The ratings will be usually displayed on the electrical appliances or apparatus itself.