When you first create your account and have access to the site, you'll go to your Pottermore profile. Towards the top of the page, there's a bunch of dots and a few different symbols. These represent the seven different Harry Potter books and the chapters with in. You'll need to explore each chapter to collect items for your trunk, and you can also collect Wizards Cards. You don't get a wand until about Chapter Three, but it's totally worth the wait. You'll be given a series of questions, and then your wand will choose you. If you unlock the exclusive content, you'll be able to find out what the different parts of your wand say about your personality. You'll be sorted into your house the same way; and I'll warn you right now, there are some hard questions on that quiz. It's not like it tests your knowledge, but the questions themselves are just questions you wouldn't normally be asked, so they're really hard to answer.
I won't go into any more detail, but I will say that you can brew potions and duel other wizards to earn house points and help your house win the cup.
Hope you're excited for the site, I think anyone who joins will find it really interesting :)