Portal/Chamber 10

Chamber 10 is where Portal starts to become increasingly more challenging, as you move from the learning to the testing stages of the game. This chamber is where you get to apply the laws of physics to the game, and use your momentum (usually downward) going into a portal to cross horizontal gaps.

First room
"Hello again. To reiterate... previous... momentum."

- GLaDOS

The first room is pretty simple. First notice that you cannot jump high enough to reach the first step. From there, look up and back to see the fixed orange portal. What you can do then is create a portal in a wall, then walk into the wall from a little distance away. Your forward momentum will carry you out of the fixed orange end of the portal on the panel onto the steps, and then you can go into the next room.

While not the intended method, it is not hard to use the camera to give enough height to just jump onto the step. Shoot a portal at it so it falls. It is possible that it rolls close enough to grab, but if not, you can usually shoot a portal under where it landed, and then grab it once it falls through. Another way is to crawl under the steps and shift it by grabbing it between the steps. In any case, just place it on the ground and hop on it, then simply jump onto the first step.
 * Using the camera to boost yourself

Second room
Seeing the diagrams on the ground in front of you lets you know that this second room is not converting horizontal momentum to horizontal momentum; it is converting downward momentum to horizontal momentum.

Like the last room, look above you for a fixed orange portal on a suspended panel. Walk to the edge of the pit and look down to see the only reachable floor to put portals on. Place a portal on the floor at the bottom of the drop, then fall into it. Your downwards momentum will carry you far when you exit the orange end of the portal, and you can go into the next room.

"Spectacular. You appear to understand how a portal affects forward momentum. Or to be more precise, how it does not."

- GLaDOS

Third room
The third room takes it a step further, and has you climb up to a higher level using a two-step process converting downwards to horizontal momentum.

This time there is a fixed orange end of a portal in the floor at the bottom of the drop. Once you look up, some of the wall panels will extend out. Place a portal on the extended panels (it doesn't really matter where, but as a general rule, the higher the exit portal is, the further you'll go), and fall into the orange portal end. You'll exit on the second level.

Once again, when you look at them, some of the panels will move forwards so that the next jump is possible. Once they've finished moving (portals can't exist on moving surfaces), place a portal on the panels again, and then fall from either level back into the orange portal end. You'll land on the third level, and be able to exit to the chamberlock.

"Momentum – a function of mass and velocity – is conserved between portals. In layman's terms: speedy thing goes in, speedy thing comes out."

- GLaDOS