Calendars
Define the working-time patterns and holidays that turn a person's employment into actual Availability.
Define the working-time patterns and holidays that turn a person's employment into actual Availability.

What you see
Each entry is a calendar — a working-time pattern (e.g. an 8-hour, 5-day week) plus the public holidays and other non-working days that apply to it. New Calendar creates one from scratch; Duplicate copies an existing calendar as a starting point so you can adjust it rather than rebuild it. A getting-started hint points you at a standard national calendar to begin from.
Why it matters, and how to use it
A calendar is what converts "this person is available" into "this many hours this week". Both People and Project Position reference calendars, so the same working pattern drives supply and demand consistently. Start from the standard calendar, duplicate it, and adjust the holidays and hours to match a region or team; then assign the right calendar to each person on the People screen.