The members of the group are automatically added to the group. The group, from an email perspective, is a distribution list (from what I understand). Hence if you name your group mygroup
and then send an email to the mygroup
email then the members will get it. Refer to this article on what an MS365 group actually represents and why you might want to use it in lieu of just a distribution list.
Also see this article comparing groups to shared mailboxes. It is dated but in my experience shared mailboxes are more common. From an email perspective they share similar goals.