pairing parameters in PBC library
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.