Here's a cutaway of the Rolls Royce Lift Fan that gives the F-35B its short takeoff-vertical landing (STOVL) capability :
Apologies for the size of this picture, but it shows the fan and intake with the doors open. 
The F-35B and F-35C test fleet is shown lined up at the Naval Air Warfare Center Aircraft Division test facility at NAS Patuxent River, Maryland. The four F-35B short takeoff/vertical landing aircraft are in the foreground; the two F-35C carrier variant aircraft can be seen at the back of the line. Photo by Andy Wolfe and Michael D. Jackson
More about it: F-35B Lift Fan Performed ‘Nearly Flawlessly’ In Operational Test At Sea, Rolls-Royce Says