Installing out side light
Chances are pretty good that the red wire is just extra (or the black wire). The two most common types of wire for lighting and outlets come in 2 and 3 wire varieties, so sometimes you have an extra wire. Try to hook up just the white and black (green to ground), and see if it works.  If not, swap the black for red.

Of course if you have a voltage tester, you can check the white/black and white/red pairs for voltage before hooking up the light.

There's a small chance that one of the red or black wires has constant voltage and the other is switched, so use a voltage detector and make sure all the power is off before splicing anything.