Hey! Are you looking for how to pay for NationBuilder. After your 14 day free trial you will be automatically billed for whichever plan you're on for the size of your nation according to our pricing structure, which you can see at http://nationbuilder.com/pricing.
You can see how much this pricing, which plan, and end your trial by going to Settings > Billing within your nation. If you need any help don't hesitate to reach out to your Community Development Representative or our Support Team at firstname.lastname@example.org.
Complete and current information on how to use NationBuilder is available in the documentation section.