The jack pads are located under holes for the factory jack. The problem is that, depending on your jack, the outer edges of the jack may hit the lower cladding. Some people actually use a hockey puck, I have always simply used a piece of wood trimmed to fit the indentation in the jack pad.

Jack stand location , as the other poster stated , depends on what you are working on. You are trying to find a solid piece of frame.

Just curious, what are you fixing that requires going under the car?

Steve