Hello,
How may i know what is in xxxxx.h?
Is ther many programm?
What are the arguments?
xxxxx.h is a file installed in your libraries or the default arduino system libraires.
if it's a default library then it's documented here on the arduino web site
if it's a library you downloaded, then some coders go all the way and also have on GitHub the documentation and examples but some don't and then the code is the best documentation.. just find the .h and look into it.
.h stands for "header".
Library .h & .cpp files are written in plain text so you can open and look at them with a simple text editor.