This was the "dress rehearsal," the penultimate in space exploration. Apollo 10 entered actual orbit around the moon, separated from the Lunar Module, and the LM (named "Snoopy") with Stafford and Cernan aboard decended to within nine miles of the lunar surface before returning and redocking with the waiting John Young in the Command Module (named "Charlie Brown").
The astronauts tested the LM's radar and ascent engine and surveyed Apollo 11's eventual landing site, the Sea of Tranquility. This mission also served as a test of the extensive new Apollo tracking and control network on earth.
Another first for this mission: For the first time, live color TV pictures were broadcast into our homes from space. What a country!