Best way to learn the basics about WRXs...
Go to REXNET, WRX.COM.AU, etc... and also P-WRX.
Go to the search engine.
Type in "Engine" into the search field.
Read
everything that comes under that search. But take it all with a pinch of salt. There will be contradictory information popping up in peoples posts every now and then.
Rinse and repeat for the searches : Gearbox,
TBE, exhaust, diffs, wheels,
ECU, turbo, etc.. anything you can think of.
This will be at least several weeks up to a months worth of reading.