Some groups may want people to buy a book or fill out a form once they've joined the group. Set up an automation to send an email to a person when they join a group.
Note
The following steps require permissions in People and Groups. This can be a collaborated effort with people who have those permissions, or an Administrator in those applications can give those permissions to the people that need them.
Create an email template to send to people after they join a group. If you want them to order a book or fill out a form , be sure to add those links!

Create a list of members of the specific group.

Once you create the list, set it to automatically refresh every day from the Settings.
Click Create Automation from the Automations tab.

Choose to automatically send an email.

Tip
If you have results on your list, be sure to check the box to apply the action to current members.
Once a person is added as a member to a group, either by joining or by the leader adding/approving them, they will automatically be added to this list when it syncs.