To join an open group, select the group and click "Join group." For closed groups, submit a membership request and wait for confirmation from the moderator. If there are delays, you can contact the moderator privately. An accidental request can be withdrawn. More information is available in the linked article.
You have discovered a group you would like to join? Here's how it works:
For open groups
Select the desired group, click "Join group" or "Become a member," and you’re in.
For the web version:
For the apps:
For closed groups
Select the desired group, click "Request to join" or "Request membership," and wait for confirmation from the group moderator.
For the web version:
For the apps:
If you have been waiting a long time for a response from the moderation, simply send them a private message.
If you accidentally clicked "Request to join," you can undo this by clicking "Withdraw request."
More information about the different groups can be found under What is the difference between an open and a closed group?