You may manage teams with different responsibilities, different goals, etc., and you want to make sure there's an easy way to differentiate between those teams, and for that you have the option to change your team grouping to best fit your needs.
When you are logged in, you simply need to hover over your name in the top-right, then go to Settings > Edit Organization. Once there, find your Manager profile by clicking on your name, and there you will see towards the bottom that you have the option to have your reps automatically grouped by role, or to custom group them based on your specific needs, and this will allow your reps to appear together on reports and goals.
Once you have selected "Custom Grouping," you will then have to manually enter a team name, a quick abbreviation for the team, and then select which reps belong in said team.
Once this is done, you will now have the option of setting different goals for the reps of this new team vs. anyone else you manage.