jonx1234,
Apologies for the late reply I've been here for years and only now saw the "Show new replies to your posts" option. Doh!
As for the wehn to use it part of your question, most recipe will tell you when to add it. :-)
Also, I've found that it's best to make a bumload (ahem, technical term) of the spice mix, say a 1/2 cup of each ingredient and store it in an airtight jar. If you're making more than three curries a week (like me) then it's just a great time saver to not to have to keep mixing smaller rinky dink amounts of something you need all the time.