Final answer:
The 'Member Of' tab in the properties window of a user account is used to add the user to new groups or remove them from existing ones.
Step-by-step explanation:
To add the user account to a group through the properties window of a user account, you would use the Member Of tab. This tab lists all the groups that the user is currently a member of and also allows you to add the user to new groups or remove them from existing ones. The other tabs like General, Profile, Account Details, and Account name serve different purposes such as displaying general information, setting user profile paths, and changing the account name, respectively.