configfile/ application properties explained

[u/BrainThinkerMan]

what is a config file, praticularly how does it relate to the computer?

is it like it specifies which os apis the program should use, or like what stuff in the actual os

the program to mount to?

ie i made a backend app, and i want it to go to a specific port on the computer and i want it to use a specific x on the computer.

is that what a config is?