the first step to a good POD is a good template (e.g. Module::Starter::PBP).

the second step is a good, intuitive API. if your API is good, a useful (meaning not too long and covering enough to start using your module) SYNOPIS section should be possible. I always look at that example code and then search for the functions I need.

Explain that functions in detail: the parameters, return values and exceptions. Your question was probably how to do that right? It is not important as long as you write it down in a clear and consitent way. Maybe look at mature modules like DBI, CGI. Provide example(s). If the examples section for a function needs to be long to cover all functionality, you should probably refactor your code.