pairing parameters in PBC library I would like to know what are the pairing parameters of PBC library and what are they used for? Here an example where they are used.

I noticed that we can give any file in the param subdirectory. Is there any difference or change if we use one file unstead of another?
the parameters define which curve is used, which has consequences on security and efficiency.

To decide which curve type you need, go to section 8 of the PBC manual and read the paper "pairings for cryptographers"

then PBC provides functions to create your curve (i.e. param files):
https://crypto.stanford.edu/pbc/manual/ch05s01.html

But you can skip this step by directly using one of the curves already provided in the param directory.