Get up high by the fan and fling yourself to the Control room with the ramps to the other side. Reunite with Glados (which activated a button). Now fling yourself again, but aimed for the exit elevator.
New element, Orange Gel! this gel makes you move faster while moving on it. Setup a runway of speed gel from the back wall over the ramp, and use that to jump the gap. Keep doing that until you reach the cube, grab it and take it back to the start. Put the cube on the button and run up to the exit.
Put a portal on the ground under the button for the door. Jump down and run along the speed gel into a portal so you fling up to the button.
Make a runway with the speed gel, and drop some blue gel from the white wall above the end. Setup some portals on the pillar so you can run down the runway and fly through the portals to the exit.
Make a ramp on the long platform on the right side of the picture, and make sure to get some gel on the platform above. Fling yourself over to the cube.
Get some blue gel on the top platform by the pressure button, and then flip it over by leaving the cube on the pressure button. Setup a new fling at the ramps further up from the first runway, and fling from them.
Beta tests complete! Make your way to the next test area.
We've got a new gel, and it's all over the place. White gel allows you to make portals on any surface covered in it. Portal up to the pathway where the white gel is spraying, and jump from there onto the blue gel.
Run down the speed gel to avoid being crushed, but time it well. Put a portal on the ramp outside and use the speed gel from before to fling yourself to the Gamma tests.
Use portals to spray white gel EVERYWHERE. Once you've sprayed some out through the grills, escape by using portals. There will be a ramp nearby. Get the white gel and cover the ramp with it.
Spray white gel over the inside of these two pillars, so you can move your portal up further and get more on. Keep doing this until you can portal up to the platform above. From there, setup a fling on the ramp.
Climb up the elevator shaft with portals, and setup a fling in the middle on the elevator. Keep flinging until you get high enough to fling to the exit.
Portal up to one of the beams and place a portal on the ramp. Then fling yourself up to the next floor.
Keeping the portal on the ramp you used, put the other portal under the blue gel so it lands on the next ramp. Fling yourself like just before you go up to the next floor.
Place the portal from the ramp on the white ground and then jump down through the other portal down the bottom. While at the height of your fling, place a portal inside the next floor, and then portal into there.
Setup the runway I have in the picture and run down it to get to the next level. From there, set some blue gel up on the white patch of ground, and take the runway again to hop across to the next area.
Portal up to the area in the picture with help from the white gel. Then portal the white gel into the fan pipe so it gets everywhere. Then you can use portals to get to the top and out of this pipe.
Fling yourself into the small room in the top corner and press the button to activate the lift back into new Aperture!