Yes is you are going to have a member based site a database is almost a necessity. Therefore the reason for the ppopularity of MySQL. So you need to have a databse with a members table and you would save all the variables from the data entered via the HTML form page into the various table.
Suppose you had a table named members and it has the columns of username, age, city,state,country, email,zipcode, and other data, it chould also have a member_id field which is usually auto incremented (meaning that each time a new orw of member data is added it assigns the next sequential number to that new member and ensures that there is a field that is unique..
Try going through the link to the book , it is easy to read and has practical examples that is easy to follow and actually do.