The Group tab in the Contact Record shows you all the groups a contact is in, whether these are normal groups, or exclusions.
As you can see above you will find a list of all groups the contact is in.
In this tab you can add them to a group, or exclude them from a group they are already in.
Please Note: If the contact is in an included group within a group, it will not show the name of that overall group here. It will also not show if they are in a group based on a group rule.