There are three ways to choose the audience to which you want to assign content:
Throughout your company:
If the assignment is sent to everyone in the company, it will be received by everyone. If a student joins your group after you've given them the assignment, they'll be enrolled in it as well, as long as the due date is still in the future (they won't be given anything from the past).
A certain group (s):
Use the drop-down option at the top of the screen to create a team assignment. By navigating to the Teams area in the left-hand navigation, you may also establish new teams and go to current team pages.
A specific person (s):
When you give an assignment to a specific person or group of people, the assignment will only be available to those people.
