A week (or month, or year) is not just a quantity of days; we think of weeks (months, years) as starting on particular dates. So Calendar mode provides commands to move to the beginning or end of a week, month or year:
These commands also take numeric arguments as repeat counts, with the repeat count indicating how many weeks, months, or years to move backward or forward.
By default, weeks begin on Sunday. To make them begin on Monday
instead, set the variable
calendar-week-start-day to 1.