A slug is a referent within a URL to a specific are of content on your site, in this case to a specific page or canvas in your Showit site. In some instances such as creating custom URL links or linking to a specified area of your site. Here is how you find those slugs needed to setup those links.
Page Slug:
To find your page slug simply go to the site panel on the left side of the Showit interface and choose the site tab at the top. Then click to select the page you wish to find the slug for.
(for larger image: Right Click>Open Image in New Tab)
With the page selected look to the properties panel on the right side and under the page info tab look for the page slug.
Canvas Slug:
The process is almost exactly the same for a canvas slug. In the site panel click the page tab and select the canvas you want to find the slug for. Then look to the properties panel and under the canvas option locate your canvas slug.
(for larger image: Right Click>Open Image in New Tab)
Note: Not all page and canvas slugs will be exactly the same as the page or canvas name as they happened to be in this example. Always be sure to double check your slug if using custom links so you don't have any broken links in your site.