A shortcut is simply a very short redirect for a long page name. This allows people to type just a few letters in the Go box in order to get to their desired page. Shortcuts are commonly used for pages in the CarlWiki namespace, in which case they are prefixed with CW:. For example, CW:S is the shortcut for this page, thus saving people the trouble of typing CarlWiki:Shortcut.
For stylistic reasons, shortcuts should be all-caps. If possible, they should be the initials of the page.
In order to create a shortcut, all you have to do is create the proper redirect. Do this by typing the name of the shortcut you want to create (such as CW:S) in the Go box, and then clicking "Create this page." Then as the page text, type:
#REDIRECT [[Target Page]]
Replacing [[Target Page]] with the name of the page you want the shortcut to go to, in this case CarlWiki:Shortcut.
Then you should add the shortcut template to the target page, so people who visit it will know the fastest way to get there. Do this by putting, at the top of the page:
Where SHRTCUT is the name of the redirect page you just made. In this example, it would be CW:S.