IncompleteOfficial response from Taylor Pineiro
Can you specify what you mean by accessing your friends website?
If you're a control panel user you can log in to the control panel via slug.nationbuilder.com/admin.
The slug is the name of the account. If you're not a control panel user, but just want to log in to the front of their website, there should have a log in normally located at the bottom of the page.
If they've customized, it may be located elsewhere. Please let us know.
Complete and current information on how to use NationBuilder is available in the documentation section.