This is a wonderful painters tool, but in hands of a novice, you can tear up your wood and cause leaks in the home.
I use a 3200 PSI with a fan tip. I know how far back to hold the wand to be sure that I am not damaging any wood.
For you, I would suggest that you rent a sprayer, say 2200 PSI and get a fan tip. Then fire the thing up and start on a out of the way area and experiment with the distance. I would say that one foot away would be a good start.
Never aim around windows or joints or upward into siding. always aim downward.
Do not stay in one area too long as you will gouge out the wood. This baby is powerful and with any dings you make, let the wood dry out and just spackle in the areas.
DO NOT PAINT OR PRIME BEFORE YOU ARE SURE THAT THE WOOD IS COMPLETELY DRIED OUT. IF YOU PAINT TOO SOON, IT WILL PEEL OFF AGAIN.