Smartcockpit used to have a copy of the fcom. The FCOM format has recently changed so don't bookmark any pages.
As I previously posted the Airbus can be very different under the skin depending on age and operator but the basic systems haven't changed too much. Remember it is just an arliner that has had computers inserted to automate many of the functions These are 1980s computers that recognise yes and no but not maybe, i.e it works, or it doesn't and you cannot coax it to change its mind.
The FCTM has some background info about some of the systems..
If you are starting a course soon then the course provider should provide documentation for you.Send me a dm if you want to know anything specific.