This one's easy: play the game.
In my teenage years, I remember my then-group having trouble learning Shadowrun, so one weekend I brought the book over to a friend's house, we made characters as we learned how to make them, and we learned everything else while playing. So, for example, we didn't know how combat worked until a fight broke out, then we pored through the book to see how we determined initiative, tried to hit things, tried to avoid getting hit, and so on.
Though I've only played it once, I loved that the adventure in Edge of the Empire's Beginner Game teaches you the rules while you play, and I think all RPGs should have something like this (I know we're doing this with the intro adventure for Dungeons & Delvers). That way you don't just have one guy figuring it out and then teaching everyone else: everyone at the table can learn together.
Also, I think it's useful to see how the creator of a game handles various things (or what various things in the game were intended to do): for example, if Dungeon World had more/better examples, there probably wouldn't be a fan-made beginner's guide to the game.
A Sundered World: Player Fragments, the first supplement for A Sundered World, if finally out!
The Paladin is technically the sixth "core" class we've provided an alternative for. If you interested in an alternate class that isn't merely a half-assed reskin, check it out!
By fan demand, we've mashed all of our 10+ Treasure volumes into one big magic item book, making it cheaper and more convenient to buy in print (which you can now do).