I had the same problem and I ended up with your question here hoping I get an answer. But after trying it out on my own, I figured it out. So, I hope this is still helpful to you and others:
Once you install BuddyPress, on top of your admin panel, it asks you to run installation wizard. Clicking on it takes you to Buddypress setting. Just go over each tap and click on save and continue until it finishes. Then you can use Buddypress.
I also figured out I need to instal bbpress plugin as well. I am not sure you can do without it or not (hope someone else advise us on that) but It runs good with Buddypress. It also gives you 3 option tabs on the left side-bar in your admin panel which are “Forums”, “Topics”, “Replies”.
I am still experimenting these plugins, so that is all I know so far.
Hope this helped