If you installed the demo data, you've got 2 forums built on bbPress. You can find the link Community > bbPress Forums > Forums page in the main menu:
Here you will find the next forums:
The first forum 'Hiking Route' is an example of a group forum and related to the same group 'Hiking Route'. The forum looks like the following:
Pay attention that only group members can create new topics in this forum. So, once a user joins a group, he can create his own topics:
The second forum 'Tourist destination' is an example of a regular forum, which looks like the following:
In regular forums can participate every user of your site and so create new topics here.
When your users create their own topics, they can find them under Community > Users forum.