What do you mean Piet, by different forum sections? Are you talking about the categories?
Go into your ACP, scroll down to Forums & Moderators. Go to Add new Forum.
On the right, fill in all of your information. If this is going to be a category, then where it says Parent Information, select None.
Scroll down to Posting Options > Act as Category > Yes.
Set your permissions, then save.
Now to add a forum to this category. Click on Add New Forum again, Do all the same stuff, but where it says Parent Forum, click the drop down menu and select the category that you want this forum to be in. Then down where it says Act As Category, select no. That makes in a forum within the category