Welcome back to NationBuilder! Connecting your custom domain to your nation is covered in this FAQ.

In particular, take a look at the instructions portion of the FAQ: http://nationbuilder.com/can_i_use_my_own_domain_name#instructions

The first step is pointing your name servers to NationBuilder, next you connect the domain to your nation, and finally, you connect the domain to a specific website within your nation. If you run into specific problems while using the instructions, please let us know by posting another question here.