Short answers, pulled from the story.
The Battle of Salem Church occurred on the 3rd of May 1863 and continued through the night into the early hours of the 4th of May 1863. Major General John Sedgwick led his VI Corps out from Marye's Heights on the morning of the 3rd of May 1863 to link up with Joseph Hooker at Chancellorsville.
Confederate General Robert E. Lee directed operations while Lafayette McLaws division and Richard H. Anderson division provided defensive lines against Union troops. Jubal Early recaptured Marye's Heights and attacked Sedgwick main lines at 7 a.m. on May 4, while William Mahone brigade joined McLaws position shortly after noon on May 3.
Major General John Sedgwick commanded about 23,000 men moving along the Orange Plank Road before casualties exceeded 5,000 men within his corps. The Union force eventually faced 25,000 Confederates with only one bridgehead for escape while holding a six mile long line by 20,000 troops.
The battle took place near Salem Church in Spotsylvania County where Union troops halted before nightfall on the 3rd of May 1863. Confederate forces defended positions west of the church while Union troops retreated across two pontoon bridges at Banks Ford after dark on May 4.
Union commanders recognized they could not sustain further attacks without risking total collapse after facing three directions simultaneously by 11 a.m. on May 4. Joseph Hooker ordered the main body of Union army to recross the Rappahannock River during the night from May 5 into May 6 following the failure at Salem Church.