Garam Masala is a staple spice of curry-cooking in India. It is a general blend of curry spices that form the basis of the flavour of any dish. Chilli is generally added separately, according to taste. You can think of garam masala as curry powder, without the chilli. Also, garam masala does not usually contain garlic or ginger: just spices.
Directions
In general, garam masala is easy to use. You generally add it to the cooking at the same stage that you would add the liquid, and add any chilli as required. Continue cooking according to preference, and the curry is complete.
Whole garam masala has a particularly fresh taste, because the idea is that you grind it immediately prior to use. This releases the flavours at exactly the right time.