At the bottom right of every post, you see a "Like" link.
"Like" is a simple way to show your feedback to a particular post. You can use it to say that you liked the post or to say thank you!
When you click on the "Like" link, it displays at the bottom of the the post that you liked that post. It also adds to the total number of likes that particular thread has received, which is shown in the top right of the thread.
In addition, likes also show up on the left pane of your profile page. It shows the likes you have given and the likes you have received.