A group is a label you give a set of customers so you can find them, and message them, together. BeNotely already knows who's due back and who hasn't been in for a while; groups are for the things only you know.
Making one
On the customer list, open Groups and choose New group…, or tick some customers and choose Add to group, then New group… to put them straight in. The group shows up for everyone on your team.
Adding people
From a profile, use Add to group under Groups. From the customer list, tick several people, or Select all to take everyone your filters found (say, everyone who bought a brand), and add them to a group in one go.
Using a group
Filter the customer list by a group to see just those people. Start a campaign for the group and only they receive it; see Campaigns. Tick them and choose Create promo code for a code only they can use. Remove someone from a group from their profile; delete a group and nobody is deleted with it.
What's the difference between a group and a segment?
A segment, such as Lapsed or Regulars, is worked out for you from what people do, and changes on its own. A group is a list you keep by hand. Both can be messaged.