DATETIMEFROMPARTS Function was introduced with SQL Server 2012. This function is used to get DateTime value from Year, Month, Day, Hour, Minute, Second and MiliSecond values.
Syntax:
DATETIMEFROMPARTS (Year, Month, Day, Hour, Minute, Second, MiliSecond)
Example:

Declare @Year int = 2015
Declare @Month int = 6
Declare @Day int = 9
Declare @Hour int = 23
Declare @Minute int = 59
Declare @Second int = 59
Declare @MiliSecond int = 0

Select DATETIMEFROMPARTS (@Year, @Month, @Day, @Hour, @Minute, @Second, @MiliSecond)

Result:
June, 09 2015 23:59:59