If you are using with Google Calendar, you have to add a calendar from the browser. Please see the Create a new calendar on the Google. You can create a calendar on your smartphone.
1. Open Google Calendar.
2. Please tap the Desktop at the bottom button. Please change the Display mode to PC.
3. At the left, next to "Other calendars," tap the + button, and then Create new calendar.
4. Add a name and description for your calendar
5. Tap Create calendar.
If you create a new calendar, it will be synchronized and displayed in this app.