You need to enable moderation in the admin/spam section. In there you'll find the following options:
- Use moderation for anonymous posts
- Use moderation if user not yet approved
- Use moderation for users with few points
- Re-moderate posts after editing
- Email me when a post needs moderation
- Time to show on moderated posts
Then you can approve or reject the posts from the admin/moderate section or when displaying the post itself, as there are approve or reject buttons added to them.