There are three ways your community members can join groups in Heartbeat:
For paid groups, use upsells. If joining a group requires a purchase, set up an upsell on your Offer to ensure that members subscribe before accessing the content.
Join a group through onboarding
If you want to invite new members that haven't joined your community yet to a specific group, you can use a Sign Up Page so they can go through your onboarding before joining the group.
Here, you can customize your onboarding to suggest specific groups to your new members during onboarding.
Join through My Groups
Members can view the groups they are part of and/or join joinable free groups by going to Account Settings > My Groups.
Join through Threads
Admin can create a post inviting members to join a group. To do this, type in $join on a chat or thread and then select the group you want to tell members about.