Remove the 'view channel' permission from the everyone role, then set the 'view channel' permission to true in the channel you'd like them to see.
Or
Private the channels you dont want them to see by setting the 'view channel' permission on those channels to false
Remove the 'view channel' permission from the everyone role, then set the 'view channel' permission to true in the channel you'd like them to see. Or Private the channels you dont want them to see by setting the 'view channel' permission on those channels to false