Short answers, pulled from the story.
Apollo 6 launched on the 4th of April 1968 to test the Saturn V rocket's third stage known as the S-IVB. Engineers placed a Lunar Test Article designated LTA-2R inside the vehicle to simulate a real lunar module without landing gear.
Pogo oscillations shook the vehicle while thrust variations caused g-forces reaching plus or minus 7.5 Gs which exceeded the design maximum of 6.6 Gs. Cross-wiring between engines in the second stage led to cascading shutdowns that forced remaining engines to burn longer than planned.
The spacecraft entered the atmosphere at 36,000 feet per second and landed 100 miles from the planned touchdown point north of Hawaii in the North Pacific Ocean. Recovery ships lifted the capsule aboard USS Hornet ten hours after launch.
Corrective actions were taken within weeks of the flight following quick analysis by the Senate Committee on Aeronautical and Space Sciences. Engineers filled cavities in valves with helium gas and replaced metal bellows with rigid bends to prevent vibration failures.
Public impact remained low due to Martin Luther King Jr.'s assassination occurring on the same day as the launch. President Lyndon B. Johnson announced he would not seek reelection four days prior which shifted national attention away from the mission.