The Account section is accessible to your school's Populi Account Administrator(s); the Invoices/Payments view is also available to your school's Billing Contact. It lets you control general settings for your school's Populi setup, security, and appearance, as well as download data backup files, monitor various account usage stats, and use some high-level reporting tools. You can even set up a localization—a translation of Populi for your users who don't speak or read English.
To get to the Account section, you need to be listed as an Account Administrator or Billing Contact. If you're listed for either, you'll see the Account link next to the orange Help button in the upper right of the screen.
Every school has at least one Populi Account Administrator (AA). The AA is a high-level Staff member who ought to have access to the sensitive settings and information in the Account section. In other words, don't hand out this access willy-nilly! If possible, it's best to have two AAs, and also good to keep this access restricted to those who need to have it.
AA's are initially set up by Populi staff during implementation. After that, only AA's can add more AA's by going to Account > Security.