Short answers, pulled from the story.
The Union army suffered 12,653 casualties: 1,284 killed, 9,600 wounded, and 1,769 captured or missing. The Confederate army lost 5,377 total. On the northern flank at Marye's Heights, Union casualties outnumbered Confederate by roughly eight to one.
The Union loss stemmed from a combination of delayed pontoon bridges, which gave Lee time to fortify his position, and Burnside's decision to launch repeated frontal assaults against the entrenched Confederate stone wall at Marye's Heights. Seven Union divisions made fourteen charges, all of which failed. Franklin also failed to exploit a temporary breakthrough on the southern flank by not committing roughly 20,000 idle reserve troops.
Major General Ambrose Burnside commanded the Union Army of the Potomac. He organized his force of 120,000 men into three grand divisions led by Major Generals Edwin V. Sumner, Joseph Hooker, and William B. Franklin. Burnside had assumed command on the 7th of November 1862, replacing George B. McClellan at Lincoln's order.
The Sunken Road was the Telegraph Road running along the crest of Marye's Heights, protected by a four-foot stone wall enhanced with log breastworks. Confederate infantry stood four ranks deep behind it. Union troops advancing across open ground were cut down before reaching it; the closest most soldiers got was within 40 yards of the wall.
Richard Rowland Kirkland, a Confederate sergeant with Company G, 2nd South Carolina Volunteer Infantry, was nicknamed the Angel of Marye's Heights. After obtaining permission from Brigadier General Joseph B. Kershaw, Kirkland carried canteens of water to wounded Union soldiers lying on the field in broad daylight on the 13th of December 1862, without a cease-fire. He is memorialized by a statue by Felix de Weldon at the Fredericksburg and Spotsylvania National Military Park.
The Battle of Fredericksburg involved the largest number of armed men ever to confront each other in a single Civil War engagement. The Union Army of the Potomac fielded 114,000 engaged troops from a total of 120,000. The Confederate Army of Northern Virginia had 72,500 engaged from nearly 79,000 present.