Adding a sprite icon is not explained

We noticed the gift_icon in the code on the home page....then we noticed that there are more to choose from:

http://votewimberger.com/wp-content/themes/uf-spirit/ui/sprite.png

How do we display each of these? Also, can we add more icons? If so, how?

looked at forums and nothing comes up for me so far? Thanks for any help.