This can be done in two scenarios:
You want to give only specific members access to the forum.
In this case, make sure you choose a Membership Plugin in your mix that integrates with BBPress or with any other classic Forum Plugin.
You then use a Plugin like Nav Menu Roles to add a menu tab and only show the Forum menu link to your Members.
In this scenario, anyone that buys a course gets access to the specific forum as well. DONE!
You want to have a Public Forum that is not bound to any Membership.
In this case, just use BBPress as it comes. Install it on your domain or on a subdomain (for example, forum.yourdomain.com) and simply add a link to it on your menu. This makes it so that anyone can access the forum.
We personally advise against running a forum on the same domain where you host and deliver your learning related content, but ultimately that will depend on your setup.