Before you remove the cap on the power steering fluid reservoir, take a rag and clean the cap and the area around it well. Even a small amount of debris can really foul up your power steering system (this goes for any hydraulic system, like a clutch or your brakes).
With the cap off, slowly begin to fill the reservoir. It will rise quickly since the system holds very little fluid. Fill it to the MAX or FULL mark that corresponds to the engine temp (hot or cold).
Be sure to replace the cap and tighten it up before you hit the road. Well done!