The 'User Registration Fields' page lets you define what information you collect from new members during registration. For each field, you have the choice of displaying it or requiring it. (Please keep in mind that 'Required' only works if 'Displayed' is checked.)

Extra Fields - If you would like to collect some other piece of information that's not included in the list, just enter a descriptive title (Shoe Size, Dog's Name, etc.), choose 'Display', and the new field will be added to the registration form. 'Extra Field 1' appears above the member's information at the top of the form and 'Extra Field 2' and 'Extra Field 3' appears below the member's information.