Its very simple, but it took some time to figure out, and several visits here, that taught me nothing.
Go to the menu My Account > Groups > My Groups
You’ll get a long URL with /my-groups/ at the end of it.
Replace “my-groups” with “create”, hit return, and you’re good to go.
I couldn’t get buddypress to do anything more than show me a homepage. All the other pages and functions came up with an error message saying page not available or some such.
It is installed properly.