By selecting the sidebar layout you can set a sidebar or a fullwidth layout. If you choose the Sidebar layout, you can set the preferred widgets areas that you want to be displayed in the sidebar.
You also have the option to hide the sidebar on topic pages and display it only on the main page of the forum.
You can use the default page for forums or you can select a existing page as well. In the latter case, you can make use of the available extra settings options (video, paralax header, header slider, etc..).