In order to access your NationBuilder control panel simply login to your website using the email and password that you setup when you created your nation. As an admin, you will see a link in your supporter nav (side bar) to the NationBuilder control panel, clicking here will take you to your control panel dashboard.

You can also use the /admin slug to login directly to your control panel. That would be: [name].nationbuilder.com/admin

In order to allow other people on your team access to your control panel you need to change their permission level to staffer. From the control panel go to the People tab or search their name, email, or twitter in the search bar. From their personal profile page click the Edit tab and change their permission level to staffer. Now they will have the same level of access to the control panel as you do.