You don't. You upload the files to your public_html folder. You can upload the compressed file/archive and use the Decompress function in the cPanel File Manager to make that process go a lot more smoothly. The MySQL database is just where the forum content will be stored once the forum software is installed.
You will need to create a MySQL database and a database user on your account first if you haven't done that already. See the page "
How to Create a MySQL Database and User" page in the x10Hosting Wiki for instructions.
Once your forum software is uploaded to the server, just follow the installation instructions in the
phpBB documentation. Your database server name will be
localhost, and the database, username and password will be whatever you created in the step above. The rest of the setup process is pretty self-explanatory, but you can use the documentation to ensure that you understand what the setup process is asking you to do.