lines that begin with "//" are comment lines. Blank lines and comment lines are used to add readability to the code but are not required for it to execute.
{$config['MINIMUM_AGE']} and {$config['BASE_URL']} are variable strings which the base php software populates with data from your forum configuration.
{$config['MINIMUM_AGE']} -- is taken from Control Panel > Registration Settings | Age Verification > Minimum Age Required
When you enable the Age Verification feature, it will display a notice to them of why they are not allowed to create an account. For example, If your forum has content on it which would not be appropriate for persons under a certain age, or if you only wanted to allow people over a certain age to register -- such as a dating site.
{$config['BASE_URL']} - is taken from Control Panel > DB, Paths & URLs | Paths & URLs > Relative URL to Main Directory
This variable is used for the relitive url on your websites main directory path. Some websites set use "/" and install their UBB.threads in the root of thier domain. Some websites place each of their scripts in to directories which make sense for categories, such as /forums or /threads or even /ubbthreads. And finally, Some websites prefer to use absolute paths. So they would enter their entire url (
http://www.EXAMPLE.com/forums ) in that box -- Duplicating "Full URL to Main Directory " within the "Relative URL to Main Directory" entry box.