Overview
A group is a collection of members, these members are in the same tier and have the same preferences. An example of a group would could be "Red Wine Only", or even combine multiple preferences, like "Red Wine Only / Six bottles".
When a tier is created you will have 1 group to begin with. Additional groups are created by additional preferences, the more preferences you have in your tier the more groups possible. When your members can only choose from either Red's Only or Mixed then you'd have 3 possible groups. If you then add in a quantity preference of 3, 6, and 12 bottles then you now have 7 possible groups.
Edit
You can edit the group name at any time via the Tier Settings page.
Remove
To remove a group you have to first remove the preference that created the group. For example if you want to remove the 12 bottle groups then you'd need to remove the 12 bottle preference. If a member can't choose a 12 bottle preference then there will be no 12 bottle group.
Admin Only
If you have special clubs then you set a group to only be available via the admin portal. This way a member can only be in that group if they are assigned by the club admin. This could be used for Friends and Family groups or for special offerings.