[gallery]
You can use this page to test the Theme's handling of the gallery shortcode, including the columns parameter, from 1 to 9 columns. Themes are only required to support the default setting (3 columns), so this page is entirely optional.
One Column
[gallery columns="1"]
Two Columns
[gallery columns="2"]
Three Columns
[gallery columns="3"]
Four Columns
[gallery columns="4"]
Five Columns
[gallery columns="5"]
Six Columns
[gallery columns="6"]
Seven Columns
[gallery columns="7"]
Eight Columns
[gallery columns="8"]
Nine Columns
[gallery columns="9"]