Excel has a number of built-in date and time functions. The following are the most popular. "Date value" can be a entry in the function or it can be a cell reference
=Now() Returns the current data and time
=Today() Returns the current date
=Month(date value) Returns the month number of a date. If A1 contained 12/16/04, then Month(A1) would return 12
=Day(date value) Returns the number of the day in the month
=Year(date value) Returns the year of the date value
=Weekday(date value Returns the day in the week as a number from 1 to 7