Chamber 11 is where you acquire the ability to create red 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 red portals will exist.
First side-room
Firstly, make an accessible portal in the room you enter, and wait for the red portal gun in the middle of the next room to make a portal in the appendix area, so the blue portal looks as in the picture. Walk through, so that you're in the appendix area.
Main room 1
Now, press the button which should be situated right in front of you. Across the room a door will open, through which a portal can be made. Do that. Wait for a red portal to be opened 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
In the room you have just entered, 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 static red portal in the main room has to move around to the right place). When it has done so, make an accessible blue portal, and wait for a red 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 button in the middle of the room, where you will receive the red portal gun. Press the button in front of you and make a blue portal in the room behind the door. Now make a red 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 it can now manufacture two linked portals at once. As part of an optional test protocol we are proud to present an amusing fact: the device is now more valuable than the organs and combined incomes of everyone in <subject hometown here>.
—GLaDOS
