Overview of Favorites
In Microsoft Teams favorites allow users to prioritize some teams over others. Teams that are in your favorites list will appear above your other teams. You should favorite teams that are the most relevant and useful to you. In order to view your favorites, click on the arrow to expand the list. (screenshots)
Viewing More of your Teams
By default when you click on the teams tab you will only see your favorites. To view the rest of your teams, click on the More button the expand the list.(screenshot)
To view archived teams, click on the Gear icon and scroll down the the bottom of the screen. (screenshot).
Adding a Team to Favorites
Expand the list of all teams as described above. Find the team you with to add to favorites and click on the ellipses to expand the menu. (screenshot)
Click on Favorite. (screenshot)