Kami is from the planet Namek. Long ago he split into two entities, one good and one evil. Kami embodies all the good, while Piccolo (the Piccolo that spat out the egg of the newer Piccolo) embodied all the bad. Because of this link between them, if one gets killed they both die. Also, since Kami created the Earth's Dragon Balls, if he dies the balls cease to function.
When Goku goes to train under King Kai, Kami brings the Z Fighters together for training in the famous Pendulum Room. The Pendulum Room is the center of all past, present and future. Tien, Chiotzu, Yamcha, Yajirobe and Krillin enter there and experience first-hand fighting with Saiyans of the past. Kami teaches them all he knows and then sends them back to Earth.
Kami lives a floating tower high above the Earth where he watches over what's happening. He has some ability to see into the future and can sense the good changes in the newer Piccolo. Later he fuses with Piccolo to make Piccolo stronger.