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 start or end of a week, month or year:
Move point to start of week (
Move point to end of week (
Move point to start of month (
Move point to end of month (
Move point to start of year (
Move point to end of 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. To change which day headers are highlighted as weekend days, set the variable calendar-weekend-days.