NEW CAP FOR LEAKING OIL WELL
In June, BP placed a cap, known as an LMRP cap, over the top of the Deepwater Horizon well so oil could be collected at the surface. However, this continued to leak oil and has now been replaced with a better fitting device. NEW CAP FOR LEAKING OIL WELL
When engineers removed the LMRP cap on 10 July, oil began to freely flow from the top of the blowout preventer once more. However, the Q4000 containment system continued to take some oil to the surface. NEW CAP FOR LEAKING OIL WELL
Engineers have now bolted a new capping stack onto the blowout preventer (BOP). A series of tests will be conducted to see if the flow of oil can be stopped using the newly installed equipment. NEW CAP FOR LEAKING OIL WELL
During the test the three ram capping stack will be closed and all sub-sea containment systems that are collecting the oil will be temporarily suspended, effectively blocking the flow of oil from the well. NEW CAP FOR LEAKING OIL WELL
BP has also hooked up a floating riser pipe to the Helix Producer ship to provide a further route to the surface for oil. These will be used to collect the oil from the well once the tests have been successfully completed.
via bbc.co.uk
This is the best explanation I’ve seen. Mostly pictures therefore I actually read it. 
