SQL Server function for datetime - DATEADD

DATEADD is a date function will return a datetime value based on the number interval add to the particular date part of the specified date. The syntax DATEADD is like:
DATEADD(date_part, number_interval, specified_date)

date_part is the parameter that specifies on which part of the date to be manipulated with the number interval. You can add month, year, day and etc. You can use
MONTH, MM or M for month
YEAR, YYYY, YY for year
DAY, DD, D for day
HH for hour
SS, S for Second

For example :
SELECT DATEADD(D, -1, GETDATE())AS [Yesterday]
SELECT DATEADD(MM, 3, GETDATE())AS [ThreeMonthsFromNow]
SELECT DATEADD(YEAR, -2, GETDATE())AS [TwoYearsAgo]