Use the "Edit" button near the top of the main page to get started. Change the welcome message at the top to add some basic information about the workgroup you'll be using this forum for, information on current projects, etc.

Add any important messages you want people to see when they come into the Forum under the "Announcements" heading.

You'll want to create new pages (using the 'New Page' link) for project information, topics that you need to discuss, documents the team is currently working on, and more. Use it for project management, for example as shown in the Todo and Meetings pages. Look at Organizing your Forum for some other ideas.