Short answers, pulled from the story.
The eastern theater of the American Civil War covered major military operations in Virginia, West Virginia, Maryland, and Pennsylvania, as well as the national capital at Washington, D.C., and the coastal areas of North Carolina. It was bounded by the Appalachian Mountains to the west and the Atlantic Ocean to the east, with the majority of battles occurring in the roughly 100-mile corridor between Washington and Richmond.
General Robert E. Lee commanded the Army of Northern Virginia for most of the war in the eastern theater, taking charge after Joseph E. Johnston was wounded at the Battle of Seven Pines on May 31-the 1st of June 1862. Lee led the army through its major campaigns until its surrender at Appomattox Court House in April 1865.
The Battle of Antietam, fought on the 17th of September 1862, near Sharpsburg, Maryland, produced more than 23,000 casualties and remains the bloodiest single day in American military history. Lee's army, outnumbered roughly two to one, fought McClellan's Union forces to a tactical standstill before withdrawing to Virginia.
Stonewall Jackson's Valley Campaign covered 646 miles in 48 days of marching, fought with a force of about 17,000 men against combined Union forces of roughly 60,000. The campaign won five significant victories and withheld approximately 50,000 Union troops from McClellan's Peninsula invasion force.
The Battle of Gettysburg, fought in July 1863 in Pennsylvania, was a three-day engagement between 160,000 soldiers that produced roughly 51,000 casualties and is often considered the turning point of the war. Union General George G. Meade defeated Robert E. Lee, ending the Confederate army's second and deepest invasion of Northern territory, with Confederate forces reaching farther north than any other major Confederate army during the war.
Unlike earlier Army of the Potomac commanders who retreated after costly battles with Lee, Ulysses S. Grant kept advancing after each engagement, sliding southeast to force Lee into a running defensive campaign. Grant absorbed approximately 55,000 casualties across the Overland Campaign but inflicted proportionally higher losses on Lee's smaller army, losses the Confederacy could not replace.