After you get a cube past a particle field, you reach Test Chamber 10.
There is an orange portal on a piece of wall sticking out above where you enter the chamber. You need to create a blue portal on the floor and fall through it. Then when you go through the orange portal, you will have enough momentum to end up on the steps.
Once you go through the next chamber lock, an orange portal will appear on another wall piece above you. You will need to use that to get beyond the gap. However, the floor and walls up here don't take portals. But you'll see if you look into the gap that the floor there is the type that takes portals, so create a blue one such that you can fall from the ledge into it. The momentum will send you across the gap.
If you are having trouble falling through the blue portal, you can go into Settings and turn on Portal Funneling, which automatically adjusts your position when approaching a portal to help you go through it.
After you go through the next chamber lock, there will be another piece of wall above you, but this time, there is no portal on it. Instead, the floor has an orange portal. Create a blue portal on the piece of wall above you, as far up as you can make it. Then fall into the orange portal.
You won't quite make it to the top level, but the wall piece will move such that you can put another blue portal on it and fall through the same orange portal as before.
After you reach the chamber lock, enter the elevator to go to Test Chamber 11.