Back in 1981 when I first heard of D&D, I got a hold of B2 Keep on the Borderlands. I had no other rulebook, and had only heard from the other kids on the school bus talk about playing the game. So with my copy of B2 and a couple of friends we played D&D.
How is this possible? We had no character creation rules or much info about the classes. What we did have were the charts in Keep on the Borderlands which gave rudimentary info. And somehow we had a blast exploring the caves, meeting the inhabitants of the Keep, and playing a very limited version of the game. This is how powerful D&D is, even at a fraction of its capability it is still an amazing experience.
I don't remember what characters we played, or much else about the adventure. But shortly thereafter I got the Moldvay Basic set and was off to the races. That Christmas I got the core AD&D rulebooks (except the Monster Manual, I got the Fiend Folio instead...weird I know) and have been playing ever since.