Here's how the forum works:
For the most part, cookies offered are Hemalurgic spikes in disguise. Anyway, first block of subforums is for miscellaneous things, Introduce Yourself, discussing the Shard and how it works, and discussing the Coppermind, the wiki for Sanderson's books.
Next is the theory boards. Cosmere theories have almost no spoiler tags except for new books, like Bands of Mourning and Secret History. Then there are theory boards for individual Cosmere books, with spoiler boards where appropriate. Then there are non-Cosmere theory boards, like Reckoners and Rithmatist. Then there are the community subforums, like general discussion, guilds, etc. And that's the basics of the Shard.