1. Substations transform voltage from one level to another. Between the power generating and consumer, electric power may flow through several substations at different voltage levels.
2. A substation is part of elektrical networks of a network operator and connects different voltage levels. Substations consist of power transformers and switchgears.
Substations are able to carry out important switching operations for the operation of the elektrical network. Besides switching in certain load situations they can also do activations for maintenance work.
From an operational view substation-busbars depict network nodes. Substations usually consist of multiple network nodes. The structure of substations is adapted to the current task.
https://en.wikipedia.org/wiki/Electrical_substation (1.); https://www.enargus.de/pub/bscw.cgi/d1712454-2/*/*/Umspannanlage.html?scope=all&search=Substation&op=Wiki.getwiki (2.)