To join a specific team, click Teams > Add team. Type the team name in the search box and press Enter. Find the team you're looking for and click Join team.
Another option is to go to the command box at the top of Teams, then type /join to see a list of all your suggested teams. Select a team to request permission to join.
First, tap Teams at the bottom of the app, then Join or create a team in the top right corner. From there, you can create a new team, browse existing teams to join, or join a team with a code (if you have one).