When you join a new team, Show Channels automatically shown in your teams list. If you know you're a member of a team but don't see it, scroll to the bottom of your teams list and select Hidden teams, find the team you're looking for select More options > Show.
Follow a channel
To follow a channel, go to the channel name and select More options > Follow this channel.
You can catch up on all your followed channels in your Activity feed. Click Activity > Filter > Following.
Hide a team or channel
If you don't want a team or channel to show in your teams list, hide it. Go to a team or channel name and select More options > Hide. This is a great way to clean up your list and focus on the teams and channels you're active in.
You can also show channels from the hidden channels menu beneath the channels list of a team. Select More options > Show.
Note: To help get you up and running, Teams automatically shows the five most popular channels in every new team you join.
Adding People to a Team
If you're a team owner, go to the team name in the teams list and click More options> Add members.
If you want, you can even add multiple people by typing the name of a contact group, security group, or Office 365 group.
People you add to a team will receive an email notification letting them know they are now a member of your team and the team will show up in their teams list.
FYI, any team can hold up to 5000 people.
Note: Go to your team in the teams list and select More options More options button > Manage team > Requests to accept or deny requests to join your team.