Grouping options determine whether your cards are displayed individually or in a group and how they are grouped.
While browsing your collection, you can change your Grouping setting using the second drop down menu on the right of the search bar. You can also set the default way your cards are grouped in the Preferences section of your Settings page.
Selecting None will display each card individually.
Selecting Printing will group cards with the same name and from the same set together.
Selecting Name will group cards with the same name together, regardless of which set they're from.