a very good link supplied by SNS.
try to buy spices from asian stores or online - i'm convinced much better quality.
having wrestled with make or buy curry powder for many yrs i now buy it and would say buy the garam masala and tandoori masala the same. (i do make my own garam but it's taken a long time to perfect and your time is best spent on other aspects).
would suggest u taste each of the spices with a wet finger so that u get an understanding of them. u need to get a coffee grinder (essential for grinding the whole spices ie coriander seed)