Multiple Addresses

I have an registration form but some users have multiple addresses. How can I have them click a button then another address field pop out?

Very easy Marie :

Make a checkbox field with admin name option-1 default unchecked.
Make a second address field in your same form, and set it to only be visible if option-1 is not blank. If the chk box is clicked, the 2nd field will appear below.

Cheers