Go into Dashboard>forums>add new
Add a forum and name it whatever you want, but you need at least one to get the forum page going (you can always delete it later).
Now go into the dashboard>topics and create a new topic. Again you can trash this later, but you’ll want to see what one looks like.
Okay, so now we have bbPress with one forum and one topic, but we’ll need to show it somewhere, so go to 3 below.