Adding Thumbnail Grid Method?

Love, Love the tutorial… but I’ve got one question.

In the very beginning the tutorial mentions the grid method as apposed to the scroll horizontal method for the thumbnails, but how do I do create the grid method.

My Thumbnails = 60px x 60px
Grid: 4 down and 4 across

Any and all advise for this amateur is greatly appreciated!

Regards,
Mpress