The Eurail pass is only valid for trains run by RENFE, except for Avlo. It is not valid in Ouigo trains either. Avlo and Ouigo only run on a few lines, as far as I know.

If you use the RENFE timetable, then you can use all listed trains, except for Avlo (it doesn't list Ouigo).

PLus that in some remote corners of ESpana there are a few minor branch lines which are run by local/regional companies, that do not accept passes. But the normal 1st time tourist is highly unlikely to use these. RENFE serves all major towns and all regions, except of course the islands. Likewise about any country in EUR has such a state-owned national train system (except the UK) and these all are in the pass scheme.

Also be aware that ALL trains in ESpana by RENFE must be reserved with additional expense-there are usually no regional alternatives without and level of service may be much lower as you may know at home. So do your homework and check if offer meets your demand!