The name simply means "hot spice", garam masala is a popular Indian spice mixture used on meats and vegetables. There are as many recipes for garam masala as their are families in India. Here is one with the most basic ingredients. You can also buy the spice pre-made most any Indian markets.
Toast coriander and cumin seeds for 3-5 min. combine with other ingredients and grind in mortar/pestle (or blender which works great for me).
Store your garam masala in a bottle for up to 6 months