Either turn to the 'Maps' section for a full Underground map, or get a map and timetable from any Underground station.
The various different 'lines' are colour coded and there are eleven in total. Trains run in a 'Northbound', 'Southbound', 'Westbound' or 'Eastbound' fashion and you need to establish which direction you are heading before boarding a train.
If you have loose change you can purchase your ticket from a machine, or from the ticket booth in most stations. Most stations are now automated, and you put your ticket in the slot, take it out, and walk through the open barrier.
Keep hold of the ticket, you will use it at the other end. Word of warning: Compared to other major cities, the Underground is a relatively safe place to be, when travelling sensibly. Avoid travelling alone at night, do not keep valuables on display. Be aware of pickpockets.
Information helpline open 24 hours a day, seven days a week: 0343 222 1234
The London Tube Rambles website explores what can be found within a mile of the outer London Tube stations - wonderful countryside, wacky architecture and more in the most unlikely places.