Promoting a MangoApps community is done through embed sharing or by using a link. When using an embed code, this can be done inline to display the join dialog UI on the site, or as a pop-up dialog that will display upon pressing a join link. When sharing externally to social media or other sites, a direct link would be used, taking users to a community page to request to join.
For public communities and groups, users are automatically approved as a guest user upon submitting their request to join and will get a unique email login link. For private teams, however, the request to join goes to team admins and the user is added and receives the same unique email login link, or a notification if declined.