how do i create a sub form when i make a selection from a radio button.

(explanation) the form has 2 option, when i select either i want to see only field relative to that selection

Example.

New user  (Radio button)

this will give me field that are only applicable to a new user

User modification (radio Button)

this will give me fields applicable to modify a user account

this can be in the form of a new page or hide or unhide certain field.