f I just want to put the camera at night at the corner of a street to get long exposure effect of the cars that are moving for their car lights, What is the focus settings I should use? Should I also focus on something?
In general, you'd want to focus on a spot midway, to slightly closer than midway, between near and far objects of interest. So, if your shot includes cars 1-4 blocks away, focus on a car ~2 blocks away.
You'll also want to increase your aperture so that more of your pictures are in focus. How much you can increase it depends on the amount of ambient light and how much noise your camera generates. Start with an aperture of ~f8 and go from there.