6 Apollo missions have landed on the Moon
In each mission, 2 of the three crew descend to the Moon in the lander, while the third stays in the command module, which orbits the Moon, then collects the other two when they lift off from the surface.
Apollo missons and dates as follows (3rd name in each list is the guy who stayed in orbit in the command module - first two names both walked on the Moon (12 in total)

Apollo 11 - July 1969
Neil Armstrong, Buzz Aldrin, Michael Collins

Apollo 12 - November 1969
Charles Conrad, Alan Bean, Richard Gordon

Apollo 13 - April 1970
James Lovell, Fred Haise, John Swigert
failed mission, returned without landing

Apollo 14 - February 1971
Alan Shepard, Ed Mitchell, Stuart Roosa

Apollo 15 - July 1971
David Scott, James Irwin, Alfred Worden

Apollo 16 - April 1972
John Young, Charlie Duke, Ken Mattingley

Apollo 17 - December 1972
Eugene Cernan, Harrison Schmidt, Ron Evans

First man to walk on Moon, Neil Armstrong
12th and last man to walk on Moon Eugene Cernan

A few reasons why we haven't been back since....
The Apollo landings were hugely expensive, NASA's budget was cut, and they couldn't afford any more Moon landings after 1972.
You gotta realise that the MAIN reason it was done was to get one-up on the Soviet Union, during the height of the Cold-War - this was how they could pump so much money into the program - after that, the justification for more funds just wasn't there.
They have hundreds of pounds of samples, so there's no pressing neccesity to go back for scientific reasons - they know that there's no money to be made from it - and they have already done the 'We were first' thing, so that's no longer a reason....

However.....
Plans ARE afoot to go back before too long - a base is planned, as a stepping stone for missions further out.
Moon gravity is FAR lower than on Earth, which means it's possible to start missions from there which will require far smaller launch vehicles than are required when blasting off from Earth.