1. Grab the end of the derailleur that is touching the freewheel, and pull it against he force of the spring until it is pointing the other direction.

2. While holding it, in the position shown in your picture, imagine the chain coming from the bottom of the chainring (where the pedals are), and wrapping clockwise around the derailleur wheel you are holding, then counter-clockwise around the other derailleur wheel, and then clockwise around the bottom of the freewheel cogs, and back around the chainring. That's the way the chain should go.