You've got a working forum with users, but you want to set up a test forum to try out some changes without messing it up for everyone.

Here's a quick step-by-step:

1. Create new database in Cpanel -> MySQL Databases. Call it "forumtest".
2. Create the database user and assign it to forumtest.
3. Create a subdirectory (or folder) under public_html, call it "testforum".
4. Install your forum software into that testforum folder. Be sure to give it the new database information you created above.
5. You would access the test forum at http://example.com/testforum∞. It would have it's own admin panel and it's own database, so any changes you make would *only* happen in the test forum.

[optional]
6. If you want real data to test with, go to Cpanel -> MySQL Databases -> phpMyAdmin -> Export
7. Export your live forum database as an .sql dump (default options, no compression).
8. Then import the .sql file into your forumtest database.

Now you have all your forums posts and settings replicated into your test database. Again, any changes made to the test forums will not happen to your live forums.