When your site is first created, we typically list your Groups alphabetically, since each department has their own system for organizing shifts/groups. However, you can change this ordering to your department's needs. Keep in mind that this group ordering is site-wide, so this will affect not only the Calendar Tab, but also the Daily Shifts Tab, forms and dropdowns, etc.
To begin, go here (Admin Tab -> Groups & Schedules -> Groups)
Once the page loads, be sure you have your desired calendar period selected in the top-right of the page. The calendar period you select here is the first calendar period that your changes will take effect. Your changes will carry forward to future calendar periods as well. You can change this to a previous calendar period before making your desired changes if you want to retroact the changes.
Next, click the "Order Groups" button in the top-left of the page.
On the page you arrive at, you can simply drag & drop the groups into your preferred order. Your ordering saves on-the-fly and automatically, no need to click a "save" button. That's it!