Portal/Chamber 11

Chamber 11 is where you acquire the ability to create orange portals as well as blue portals, and thus complete more difficult challenges; from the point at which you get this ability onwards, you have to create both ends of the portal, as no static orange portals will exist.

First side-room
Notice that that the orange portal gun shoots in three different locations. Two of these are above the mysterious-looking “floor” that will, as GLaDOS points out, kill you, and the third shoots somewhere you cannot see. So make an accessible portal in the room you enter, and watch the area just inside the portal. Wait for the orange portal gun in the middle of the next room to make a portal in an area with a solid floor, so the blue portal looks as in the picture. Walk through, so that you're in that area safely.

Main room 1
Now, press the button (the game will let you know that the same key you use to hold onto things presses this button) which should be situated right in front of you. Across the room a door will open temporarily, through which a portal can be made. Do that (the portal will not disappear when the door closes; you simply cannot see it from here). Wait for an orange portal to be shot in the area where you are, and walk through it so that you come out in the second side-room, where the energy pellet required to activate the platform in the main room is situated.

Second side-room
Briefly walk down the stairs to look at the main room from this angle. Notice that one of the locations that the orange portal is placed is directly across from the pellet receiver. So make a portal on the scorch mark where the pellet hits the wall. Wait for the pellet to go into the pellet receiver (this may take some time, as the orange portal in the main room has to be in the right place when the pellet moves through the blue portal). When it has done so, make an accessible blue portal, and wait for the orange portal to be created in front of the moving platform. You can then walk onto the platform.

Main room 2
Take the moving platform to the middle of the room, where you will receive the orange portal gun. Press the button that appears in front of you and make a blue portal in the room behind the door. Now make an orange portal where you entered the room to get on the platform the last time, walk onto the moving platform, and enter the portal. From the room you enter you have direct access to the chamberlock.

"The device has been modified, so that it can now manufacture two linked portals at once. As part of an optional test protocol we are pleased to present an amusing fact: the device is now more valuable than the organs and combined incomes of everyone in."

- GLaDOS

Note that from now on, you have the option of blue or orange portals, and so the colors listed in this guide do not have to be the color you shoot. In this last part, for example, you could shoot an orange portal in the final room and a blue portal that you walk from the platform into, and you will achieve the same result. Simply make sure that the right portal connections are made; for example, do not shoot a blue portal in the final room, and then another blue portal next to the moving platform, as you will have gotten rid of the portal in the final room. Notice that whatever color the last portal you shot was, a small oval appears next to your aim on the appropriate color’s side. This appears based on the shot, and not on the success of the shot, so that if you try to shoot a blue portal onto a non-portalable wall, there will still be a blue oval next to your aim. This can be very useful if you ever forget what color you just shot.