2
IMHO: If you don't have a lot of traffic, I suggest the easiest way to manage it is to allow posts by registered users only when you set up the modules. This keeps most spammers out of the picture and those really interested in your site the freedom to post. If you make it so every post requires approval you may not get active involvement in your site - it implies the webmaster doesn't trust me to be adult like in bahviour so I won't bother. So..if you want a dynamic and active community your posts and comments should be open to registered users and you need to show a little faith in them.
If on the other hand you are happy to have a less dynamic and more static site then as you set up each forum category you need to set the moderator as webmaster (yourself) and make sure webmaster is the only one who can post without approval. (At the bottom of your forum set up). If you have already set up forum categories and subcategories go to your forum admin, click the forums tab and the edit icon (pencil) will take you to where you can change it.
HTH