First, you will need an method for authentication against your mySQL data.

A quick search provides Apache authentication with Mysql ...the examples given there will get you started down the path of getting your site to authenticate against the users in your database.

You can use the above to provide read-only access to unauthenticated users by simply changing your forms based on whether the user has logged in.

Next, you need to have the ability to have users only edit the data they enter, or have permission to edit...this will take some creativity. Off the top of my head the approach I would try is to add an extra table to show who is the owner and/or the security level of each record.

This would be used as a flag to determine if the user logged in has the appropriate security level edit the record they retrieved, or if it would be read-only.

This is just a start, but it should get you running down the road....good luck.