After your account is established - you'll get an email letting you know you're approved - you need to create a class. This will create a "virtual space" or "classroom" that is identified by a Course Token (also called a Class ID on some GENI-ACT screens).
Students will use the Token when they create their account. This puts them into that "virtual space" (class). They will then appear in your Roster. You need them in there before you can create assignments for them.
This video shows how you will create your class.