You can add new viewing tiles to a layout in one of three ways:
Viewing tiles are added in rows. For example, when editing a six-square (3*2) layout, a column of two grid squares is added when a fragment is chosen on the left or right side of the screen.
A row of three squares is added when you select a fragment from the upper or lower part of the screen.
When you select a corner fragment, both a row and column are added.