The D&D player’s handbook contain lots of information, and basically you can’t remember them all at once. Although this is not D&D’s, but it contains the features and controls you need to know in order to play the game in handy.
And as the features added in future the handbook will also updated with the playable game release, perhaps one day it’ll also has tons of pages.

Anyway, the game will be published hours later and please browse the handbook before you play in order to have a better game experience, thanks for reading!