On Primavera P6 the calendars are associated directly to the activities or resources.

A work plan is based on the time period. When a activity is created and the user determines its duration, the tool will calculate the date and hour of its conclusion.

A fundamental concept to understand:

Primavera P6 works in hours, normally a user works in days.

As indicated in the image, there are 3 (three) types of calendars on the system.

Start Page - Training Schedule - Resources