When Noah and I started playing, we just jumped in. To this day, I've never actually seen a rulebook but have heard there is something out there that is long and complicated. RTFM? No way.
Luckily, if you read the cards and start playing, most of the rules become pretty obvious. Noah played in a few junior league tournaments and we saw the basics of: cast spell, attack, respond. Things like that.
But Instants...those made no sense. You could just cast them whenever, all willy nilly and they did things. Doom Blade was the big one...it destroyed the freaking creature! But, having no idea that something called the stack existed, it turned into a game of reflexes. If I had a creature that had an enter the battlefield effect (say Thragtusk) and Noah had a Doom Blade, he would hold it in his hand and if he had it hit the table before my creature did I wouldn't get my 5 life.
It got to the point where we would be slamming cards on the table without even realizing what the other guy was playing in an attempt to get the instant's effect first. There was no way that this could be right but it's how we played.
Learning the rules has made the game more fun and sensible but I do kind of miss the adrenaline rush of slamming cards on the table.