Hi there Maggie.
Setting up PHPBB through C-Panel will not prevent you from using the database for other things, however, each of the auto installs from C-Panel requires a fresh database, so unless you have the Voyager account, you will need to purchase extra databases if you want to use more than one auto install that is reliant on having a database.
The setup proceedure for PHPBB manually is very straight forward really, and to be honest, whilst I now consider myself a moderate level user, the first time I did the manual installation, it was the first thing I had done with PHP, first thing with an online database, first program installation on my Lunar Pages account.
As long as you go step by step it need not be a problem. The other thing of course is you must have a database set up, however, this is very simply done through C-Panel. As a recommendation, the C-Panel X skin is easy to use. Have a look at your C-Panel, if it is blue in colour and says C Panel 6 near the top, I would recommend you email email@example.com and request a change to the C-Panel 'X' theme. This is much better in layout, and easier to use.
If you find any part of the How To: article confusing, let me know and I'll explain it. This will also help me to modify the tutorial to help make it easier for other people.