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.
This is a test for Jetpack's Tiled Gallery.
Install Jetpack to test.
[gallery type="rectangular" columns="4" ids="755,757,758,760,766,763" orderby="rand"]
This is some text after the Tiled Gallery just to make sure that everything spaces nicely.
[wpvideo tFnqC9XQ w=680]
VideoPress, especially as a video post format, usually provides some unique styling issues.
You will need to install Jetpack or Slim Jetpack plugin to turn the shortcode into a viewable video.