The things that show up on your app's main view are part of some seed data that is added to your database (including your test and admin users) every time you restart your app (by running grunt serve in the command line). This data is defined in /server/config/seed.js.
You can add, remove, or change data in this file, and it will be written to your database, overwriting any duplicates the next time you run grunt serve. If an object defined in seed.js is overwritten, the database will assign a new ._id property to it (we'll cover ._id properties in the next section), which may give you some issues later on in testing. To avoid this, you can turn off seeding by setting seedDB: false in /server/config/environment/development.js.