If you want to set up just a separate calendar account or your available calendar account could not be found using the Automatic setup, you can definitely set it up manually.

•          First, go to Menu > Accounts, and click on the + Add account button.
•          Skip the Automatic setup and click the Calendar section instead.
•          Select the option that applies to your existing Calendar account and click Next to finish the setup.

Note: If you don't have an online calendar account but would want to have one to synchronize your calendar online to your other devices, you can register an account for free on platforms that provide an option to synchronize just your Calendars and Contacts (such as Fruux, for example).

Read more in the Documentation: About Calendar