How to new profile field to sign up form: Buddypress
By default, wordpress MU comes with a register.php file, with the following fields:
And blog title
However, once you install buddypress, you can add more fields and get more details about your new members.
1) Login to your WPMU admin panel
2) Go to Buddypress -à Profile Field Setup
3) Click on add new field
4) Enter the field title and select the field type.
5) Click on save
6) Or you can add the prebuilt fields as well from the options.