Step by Step direction to create a Portfolio

hi-
I am getting caught up on how to create a portfolio for 3 categories.
Are there step by step directions on how to do this for this theme?

I created 3 categories but which short code button do I use make each portfolio page look like your sample on
http://themeforest.net/item/aqua-responsive-multipurpose-wordpress-template/full_screen_preview/3649588

Not sure if I need a thumbnail and regular size image, if so what sizes should they be?

Thanks for your help!