how can i add fields to registration page?

You tagged the post as 5.x but content_profile is a 6.x module - for 5.x it's much simpler to use the bio module which serves a similar purpose and adds the fields into the standard user registration form.

Of course, the bio module doesn't add the field to the Ucreate registration form. So what to do?

A simple solution is to change the ucreate confirmation message received after saving the new user, and to add a link to add a link to the standard user editing page.

Here is a patch to ucreate.module which does exactly this.

Of course a better solution would be to create a bio-like behavior which attaches the bio fields to the bottom of the ucreate registration form.

I've currently decided to uninstall this module and use the standard (bio-enhanced) user registration form - all extra fields are planted by the bio module. Also I've configured OG so that certain groups appear in the user registration form.

Marking as duplicate of #827828: integrate profile fields and #544722: Content profile support.