Syntax
DATEADD ( datepart , number, date )
datepart
Datepart Abbreviations
Year = yy, yyyy
quarter = qq, q
Month = mm, m
dayofyear = dy, y
Day = dd, d
Week wk, ww
Hour = = hh
minute = mi, n
second = ss, s
millisecond = ms

Sample
SELECT DATEADD(day, 5, StartDate) AS NewStartDate