Help need with pytest_sessionstart

Please forgive me I am new to Python and Pytest and am already having a hard time understanding some functionality. I would like to distribute my tests across my selenium grid nodes. Prior to attempting to use this package I had a conftest file containing a pytest_sessionstart hook which would run once prior to all tests. The tests wouldnt start running until it was finished, this is the behavior I'm looking for. But when I attempt to use the xdist package its being run multiple times. Not sure if its once per test or worker. I want it to run once before distributing tests across the nodes. Can anyone help explain this to me in really simple terms? Thanks.

Start with the conftest.py pytest_sessionstart hook and pytest-xdist's worker lifecycle, focusing on when the hook runs relative to test distribution across Selenium Grid nodes. Done means clearly explaining the current behavior and confirming whether a single pre-distribution run is supported or requires a scoped change.