Favorite a channel to keep it visible in your teams list or follow it to get notifications and stay up to date on new channel activity.
Favorite a channel
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From within the channel, select Favorite
next to the channel name.Or, select more channels in the teams list and then select Favorite
next to the channel.
Follow a channel
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In the teams list, go to the channel name.
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Select More options
> Follow this channel.
Source: Microsoft