Portal Chapter 5 (Puzzle 13)
When the lift door opens head through to the room with the red button. Place a portal on the ground level and one on the upper level. Go through, pick up the button and drop down to place it on the red button. Go back through the portal and out the door to the large room.
Here you have two red buttons, a platform with a cube and a light ball. Drop down and place one portal on the roof above the receptacle and the other on the wall where the light ball hits. Once the light ball enters the receptacle the platform will activate.
Place a portal on the roof above where the platform moves and the second portal somewhere where you can walk through. Drop down onto the platfrom as it moves under the portal and pick up the cube.
Place a portal on the wall next to the highest red button and one on the wall where you can walk through. Take the cube through the portal and drop it onto the red button. Jump across and stand on the second red button to open the door. While standing on the red button shoot a portal through the door to the other side. Place the second portal somewhere near and walk through to the level exit.
Next: Portal Chapter 6 (Puzzle 14)