Without knowing what you bought, that's a pretty open ended question. If it was a compendium (Monster Manual, Xanathar's, etc.), go to the Compendium home page in the Tools menu at the top of the page. Click on the sourcebook you want to read. If it was a module, create a game with that module (you can create as many as you wish), and it is readable in the form of organized and cross-linked handouts. If it was an addon, those are added to an existing game on your game's details page, and again, is readable in-game in the form of organized and cross-linked handouts