The Mercury Project was America's first manned space missions.  The flights were very short and the shuttles were small but the importance was huge.  NASA wanted to launch, orbit, and land a human with the shuttle safely.
The United States recruited astronauts and put the under test after to test to see if they were capable of being sent to space.  The 'to-be' astronaut had to be related with airplanes and have an engineering degree, 508 people were first looked at then cut down to 110.  There were background checks and there were under constant interrogation.  After all that the seven were picked and they were celebreties.
20 Unmanned missions held accomplishments of emergency escapes, sun sheilds, high altitudes, reduced impacts, temperature controls.  These accomplishments led to the manned Mercury missions and succesful missions in the future. 
Liberty Bell 7 MR-4: Virgil Grissom was launched into space July 21, 1961 after two other dates of this launch was delayed due to weather.  The accomplishments of this mission answered if the larger window would be effective, how much a human has control over, and the effectiveness of an explosive hatch.
Sigma 7 MA-8: Walter M. Schirra launched a man machine into orbit he controlled from earth.  His objective was to keep the shuttle in orbit for 9 hours and completed it.  The shuttle never landed after it was launched on October 3, 1962.
Aurora 7 MA-7: Scott Carpenter went into space May 24, 1962 for 4 hours and did 3 orbits.  His mission was to control the time in orbit and was successful in doing so.  The landing was off target but Carpenter was okay, but the shuttle had some water damage when Carpenter got out into the life raft.  
Friendship 7 MA-6: John Glen was launched into space Febuary 20, 1962.  He was the first American to orbit the earth and was in space for about 4 hours.  His main objective was to land the plane in a easily found place and that was Bermuda.  Even though some of the shuttle was damaged the mission was very succesful. 
Faith 7 MA-9:  Gordon Cooper launched this man machine into orbit for a day completing his mission on May 15, 1963.
Freedom 7 MR-3: Alan B. Shepard was the first American to go into space May 14, 1961.  He was in space for 15 minutes and accomplished the mission answering the questions weather a human can go into space and the shuttle can be handled properly. 
Information: ksc.nasa.gov