Changing New User Registration

I'm completely new to elgg programming, and as a starting project what I want to do is override the default user registration form to include one more component;

What I want to have is a "registration code" field that users will need to fill in to register an account. This registration code will be defined (preferably) on the administrator control panel, and multiple codes can be defined. These codes, upon user registration, will automatically add that user into one or more groups on the site.

I'm wondering where to start looking for how to do this. First I'll need to define the control panel section to allow an administrator to define these registration codes, then I'll need to be able to override the registration page in order to add the code field. I am so far lost in a sea of documentation.

Any help or suggestion of where to look would be greatly appreciated, thanks.

Beginning Developers

Beginning Developers

This space is for newcomers, who wish to build a new plugin or to customize an existing one to their liking