These track diagrams show you the location of trains on the railway in real-time. It's the same data as the signaller and train operators see.
Each black rectangle represents a "berth" where a train can be detected. If a train is detected in that berth, the train's reporting number (headcode) will be shown - for example, 1N01. Some trains operated by non-passenger operators, such as DB Schenker or DRS, will show an obfuscated headcode in a format such as 601A.
Where the line is blocked for any reason - such as for engineering works or due to an infrastructure fault, the signaller may put a special description in a berth. "SHUT", "BLOK" and "CLSD" normally mean the track is unavailable. "-T3-", "-XO-" or "POSS" usually mean there is an engineering possession.
Some of the diagrams also show additional information such as signal aspects - red for danger, green for any other colour, and when trains are ready to depart - a red "TRTS" indication.