NationBuilder has easy online signup with a 14-day free trial. Go to nationbuilder.com/startnow and enter your contact and billing info to get going. Once you sign up, you'll be prompted to install your account.
You'll be asked for basic details such as time zone and country that help NationBuilder customize features for you.
You'll need to enter a primary account name and email address - this should be the name and email of your candidate, campaign, initiative, business or organization, but you can easily change it later. You'll also be asked to connect your Twitter account (be sure you're logged in with the account you want to connect as the primary voice of the nation) and Facebook Page. You'll need to log into your personal Facebook account with permissions for the Page you want to connect, and you'll be prompted to pick from a list of all your pages which one you want to connect.
You'll be asked for a headline and purpose (this text will be a like a secondary headline on many of the official website themes) of your nation. You can leave the purpose blank if you want and it's easy to add later in the field at Websites > Settings > Basics > Subheadline.
You'll be prompted to create a phone number if you want one, and will be able to select an area code for that number. You can skip this and add later if you like.
NationBuilder will ask you to select default pages for your site, and you can uncheck any of these: blog, signup, volunteer signup, about, suggestion box, and calendar (events). For a full description of NationBuilder page types, check out nationbuilder.com/what_kinds_of_pages_can_i_have_on_my_nationbuilder_site You'll be able to select more pages later, and your defaults will also include core pages like Friends, Recruiting, Political Capital, Leadboards, Follows, Followers, Rules and Unsubscribe.
You'll also need to pick a website theme and style and a logo. The logo should be square and 150x150p is a good size. You can always change your website theme and style later under Websites > Theme, and you can review the available options at nationbuilder.com/nationbuilder_official_website_themes
Finally, you'll be asked to set the rules for your nation (the defaults are pretty popular), and the you'll be in your control panel, which is the nerve center of your new nation. Congrats!