This will probably be unlocked during normal play.
Once you enter chamber 6-6 turn right and put a portal on the wall and another to the top right of it on the ledge. Go through this stand on the button. Place the portal on t he ledge with you under the orange gel tube. This will create a run way.
Then place one portal on the tilted ramp and the other under the white gel tube, while on the button this will reach the opposite wall. Place a portal on the new wall and your other under the blue gell pipe. This will cover the small square in the middle.
Put a portal on the white wall you created and the other at the end of your orange runway. This will bounce you off the centre platform to the end.
The video guide starts at 1:51