Why 3 calendars?

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For some reason I have 3 calendars in Outlook 2016:

- Calendar (This computer only) my e-mail address

- Calendar (This computer only) Outlook Data File

- Calendar

Apparently when I first started entering data in outlook, I used the first one above which allowed me to enter Reminders for appointments, but did not allow me to set up color coded categories. I was experimenting with categories 2 and 3 above today which allowed me to use color coded categories, but not reminders.

Also in Outlook Today, the only appointments that show up are the ones in the first calendar.

Is there a way to use one calendar that allows Reminders and Color coded categories that will appear in Outlook Today.