The back is where the separate pieces of equipment are connected together using various kinds of sockets - often called 'ports' - and plugs or connectors. If a connector has pins sticking out it is a 'male' plug; if it has holes for pins to stick into, it is female. Original, huh? Sometimes it's necessary to convert a male to a female connector - and this needs a piece of equipment which goes by the interesting sobriquet of a 'gender bender'.
The monitor is usually connected by a 9-pin or 15-pin plug to a special socket on the processor box; the keyboard by a small round connector like a radio jack. The mouse - if there is one - is usually connected by a 25-pin connector to a plug known as the 'serial port' and the printer is normally connected to a 36-pin plug known as the 'parallel port'.
It sounds more complicated than it is. Usually the cable that comes with the printer or whatever, will only fit into one socket, so there is little scope for error. This being Britain, probably the biggest problem will be the mains electricity supply. The processor, monitor and printer will all need separate power supplies - which means wiring up the three-pin plugs that British retailers still seem to think of as some strange optional extra.