Groups allow you to easily manage your address book and send out Bulk Messages or Group Messages to a subset of people. You can create a group from the contacts in your account; there is an article on that here.
You can also create new groups and add existing or new contacts to them any time!
Just click here, go to Contacts on the left-hand side → ‘Create Group’ on the top left.
Give your group a name and hit 'Create Group'.
You can send a campaign, delete, export, and any group with the icons on the right-hand side of your groups.