The first shots of the Civil War were fired on April 12, 1861 at Fort Sumter

The first shots of the American Civil War (wiki) were fired on April 12, 1861 at Fort Sumter: 

Bombardment of Fort Sumter by Currier & Ives

South Carolina had seceded from the Union on December 20, 1860 - at that time, United States Major Robert Anderson and his force of 85 soldiers were positioned at Fort Moultrie near the mouth of Charleston Harbor. On December 26, fearing for the safety of his men, Anderson moved his command to Fort Sumter (wiki) in the middle of the harbor. 

On Thursday, April 11, 1861, Confederate Brig. Gen. P.G.T. Beauregard dispatched aides to Maj. Anderson to demand the fort’s surrender. Anderson refused. The next morning, at 4:30 a.m., Confederate batteries opened fire on Fort Sumter and continued for 34 hours. 

The firing continued all day, although much less rapidly since the Union aimed to conserve ammunition. "The crashing of the shot, the bursting of the shells, the falling of the walls, and the roar of the flames, made a pandemonium of the fort," wrote Union Capt. Abner Doubleday, the fort's second in command. 

On Saturday, April 13, Anderson surrendered the fort. The generous terms of surrender allowed Anderson to perform a 100-gun salute before he and his men evacuated the fort the next day; although no soldiers had been killed in the battle, an accidental explosion during the salute killed one of the gunners and mortally wounded another. 

Carrying their tattered banner, the men marched out of the fort and boarded a boat that ferried them to the Union ships outside the harbor. They were greeted as heroes on their return to the North.

Two days later, U.S. President Abraham Lincoln (wiki) issued a proclamation calling for 75,000 volunteer soldiers to quell the Southern “insurrection.”

The Civil War Trust's Fort Sumter Animated Map depicts the events that lead to the first shots of the Civil War as well as other important battles in Charleston Harbor.:

Fort Sumter Animated Map from Civil War Trust on Vimeo.

Here's an animated map showing the daily changes to the front over the course of the war:

Legend:

Maroon = Confederate States of America and territories

Red = Areas occupied by Confederate forces

Pink = Gains for that Day

Dark Blue = United States of America and territories

Blue = Areas occupied by Union forces.

Light blue = Gains for that day

Yellow = Border states / disputed areas.

Related posts:

Santa Claus enters the fray on the side of the Union.

It's Stonewall Jackson's birthday - here's the story of his left arm's separate grave.

The Gettysburg Address was seven score and eleven years ago.

Abraham Lincoln was assassinated 150 years ago today.

Gorgeous remastered and colorized images from the Civil War era, including Lincoln and Mark Twain

There's lots more on Fort Sumter at CivilWar.org and the Smithsonian.