This page is designed for definition of used fields of the user account.
See the image below:
Standard Fields
To use Middle Name field of the user account, select the Use Field [Middle Name] option.
Additional User Fields
You can use additional (up to 5) fields of the user account, specified here. To use some additional field, select appropriate option, and then specify the text in the Caption field. You can limit possible values of the field, enter them (use semicolon as delimiter) in the appropriate Values entry field.