For information on setting up forms in general, read here.

On the Run form builder, click to add destination, and after you select NationBuilder, enter your NationBuilder slug / subdomain (slug.nationbuilder.com). Then click the button to login. After you've successfully logged in, click the Save button. Confirm that it's connecting correctly under Status after you save.

On the form builder, you must click on the Enable checkbox to the left of the destination for all forms you want to use this destination for on your website.

If you have any Tags in your Nationbuilder account, they'll appear in your Run form builder upon successful connection. You can add Tags on your NationBuilder CMS at People > Tags > Create Tags. Back on the Run form builder, you can select a tag and then any submissions that come through the form will include that tag.

In order to add custom fields to your form, you'll first need to add those fields on NationBuilder. In your NationBuilderCMS, go to Settings > Nation defaults > Custom fields > New custom field. Make sure to select Text Field as your Field Type.

Then, open your Run form builder, click Add Form Field, and add a Custom Field (like 'Text' for example). Under the NationBuilder custom fields column, Run will pull down a list of your custom fields from NationBuilder to select from.