Is there a way to send and receive private messages on the forums and how do you do it ?

You first need to be friend of the people you'd like to contact via P/M. Click on the avatar of the people you want to be freind with, and then click on "add to my list of friends" + add a short friendship request. As soon as you and the other person are friends, you can PM him / her as long as you wish (from your profile, go to "my friends" and then there is a small icon allowing you to send PMs.

Hope this helps!