I cannot stress enough the importance of story sharing sites like Wattpad and Fictionpress for the budding author. They offer so many benefits, why aren't you on there already?
Critiques. Once you post your work on Wattpad, you can receive comments and feedback from the community. This is beyond useful as your create your masterpiece. They will not be shy to point out what needs fixing, but they will also point out what they like. Yes, sometimes it is a hard pill to swallow, but at the end of the day, your book will be better because of it. What I really like about Wattpad, is that you cannot leave a comment as a guest, so you always have to own up to what you've said. Unlike Fictionpress, which allows people to review as a guest and sometimes this is a breeding ground for trolls.
Socializing. The thing about Wattpad is that it's not just a site for books, it's also a social network. There are clubs you can join and threads you can comment and interact with. I've met some super awesome people on here, most are writers just like yourself.
Exposure. These sites can also be used as a marketing tool. Millions of people connect to Wattpad everyday and that gives you millions of chances to have your book seen. If you want your book to be at the top of the rankings, you will need to make sure you have a regular updating schedule, a catchy book cover and blurb, edit your work as best as you can, and interact with the people reading your story.
Contests. Wattpad has contests like The Wattys and Wattpad Prize. There are certain rules for each, so make sure to read them carefully before entering. These also are a great way to get your work out there.
So if you're not on there, go now and be free to write your heart out! And meet some cool people! Oh, and look for me too while you're there ;)