How to use DATEPART() in SQL ?

For SQL Server:

SELECT [ID],[RollNo],[Name],[Address],[Telephone],AdmissionDate]
FROM [dbo].[Students]

where 
(DATEPART(DAY,AdmissionDate)= '31' ) and DATEPART(MONTH,AdmissionDate)= '08' and DATEPART(YEAR,AdmissionDate)= '2014' 

order by ID desc