Sadly, topics are not quite as easy to get to as we’d like. Right now, the only way to add them is to hover your mouse over one wherever you see one you’d like to add (other questions, other people’s profiles, in the topic cloud at the lower right hand corner).
As far as ‘your story’ goes, that’s completely up to you. Some people tell a lot about themselves, some post favorite books/songs/quotes, and some people don’t fill it out at all. What I personally like to see is enough to give us an idea about what you’re like. What you do, what you know, and what you care about. But that’s just me. Welcome to Fluther! :)