Search above for a headcode (the four-character code like 1A24 that identifies a train on the network), a planning ID, or simply where a train starts and ends. Every service on the timetable has a page here, and every page has an address you can bookmark or send to someone.
Looking for what is leaving a station in the next hour instead? Use the departure boards, and click any train there to land back here. To follow a journey you are actually making, track a train. For what headcodes and planning IDs mean, see the FAQ.