Shimano, Campagnolo and SRAM have a lot of technical documents on their website. Shimano keeps them all here.... http://si.shimano.com/#/ They have compatibility tables that show their current and recently discontinued stuff. And archives that go way back. It does take some effort to get use to how they work.

Experience will be your best teacher. Learn from your mistakes. Avoid mix and match components if it's not necessary. Keep road groups together and mountain bike groups together. Though some do cross over with no issue.