Audio jacks have been around for decades and have been used in a wide variety of applications. While simple in their basic functionality, they can be used in complex systems.
Understanding Audio Jack Switches and Schematics document will help you understand some of their capabilities and will dig into the “guts” of these connectors.When looking at a seemingly simple audio jack datasheet, you will often find an array of schematics with a variation of switches and connections.
When you have read the document on connectors itself, it is a good idea to also get information on wiring between different devices. For this it s a very good idea to read the classic Rane Sound System Interconnection document. This note, originally written in 1985, continues to be still a very useful reference.