when i select date from calendar control then on label date should be startdate of week and end date of week

Use the DayOfWeek property of DateTime object.
See http://msdn.microsoft.com/en-us/library/system.datetime.dayofweek.aspx[^]
And read the part of

The value of the constants in the DayOfWeek enumeration ranges from DayOfWeek.Sunday to DayOfWeek.Saturday. If cast to an integer, its value ranges from zero (which indicates DayOfWeek.Sunday) to six (which indicates DayOfWeek.Saturday).

So I can see which value my current DayOfWeek for the CalendarControl is.
Sundayis int 0 so to set begin of week you create a new DateTime().AddDays(x);
x = value 0 - of current DayOfWeek
Well End of week should be simple for you.