The like button is at the bottom of the postbit next to the edit or quote buttons. This flags your name on this post saying you like this post. It also adds to that users like count. You can at any time remove your like. You can see any users liked and received likes on their profile. Their received likes number is also in each postbit on the top right.

This is meant to show outwardly that you agree with the post. It is also meant to remove a separate post where people add +1 as the only content of the post and quote the original post that they like. This is very similar to the facebook like system.