Hi there, Joyce–thanks for following up!
We’re fairly limited in how much support we can provide for custom development, but if you check out the section “How to Add Views” you can modify that to add categories to your list of calendar views, specifically Line 5 of the example, where the URL can be modified to be the URL of the category you’d like to add to the list.
If you’re looking for something more out of the box, you might be interested in checking out our Filter Bar plugin. It includes an option that allows visitors to filter your calendar by categories.
Cheers!
Geoff