At some point, it will occur to you to ask, "What are the current configuration settings?"
Most settings can be changed in more than one way, and some ways do not affect all users or all sessions, so it is quite possible to get confused.
Your first thought is probably to look in postgresql.conf, which is the configuration file, described in detail in the Updating the parameter file recipe. That works, but only as long as there is only one parameter file. If there are two, then maybe you're reading the wrong file! (How do you know?) So, the cautious and accurate way is not to trust a text file, but to trust the server itself.
Moreover, you learned in the previous recipe, Changing parameters in your programs, that each parameter has a scope that determines when it can be set. Some parameters can be set through postgresql.conf, but others can be changed afterwards. So, the current value of configuration settings may have been subsequently...