constraints

Hiya peops!!
Listen i was wondering if anyone could tell me whether they know the correct syntax for creating constraints or where i could find it on the net?
ThanksSearch BOL for ALTER TABLE|||Check out CREATE TABLE in BOL.

online at:
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/tsqlref/ts_create2_8g9x.asp|||Or that...

ALTER TABLE
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/tsqlref/ts_create2_8g9x.asp