Start by taking a look in the php Dealing with Forms tutorial at php.net

Then, after you see what's going on with the form interface, take a look at the PHP documentation, particularly the database documentation for MySql at php.net. The MySQL example code demonstrates connecting to a MySQL database, performing a query, then displaying the results. In your case, you would be issuing a SQL INSERT statement, rather than a SELECT statement.

Now, as far as the cpanel side of it, I have no idea as to where the data is being stored, or whether it's even available to you for direct manipulation.