Gravity
Yes. The US flag was knocked down by the bombardment and the Confederates assumed the fort had struck its colors, so they sent a party by rowboat to accept Fort Sumter's surrender. Instead, an agreement was reached whereby the Union troops were allowed to withdraw, leaving Fort Sumter in Confederate hands.
Fort Sumter
Major Robert Anderson was allowed to take the US flag which had flown over Fort Sumter with him when he left the fort.
None, although one of them came close. One of the Confederate officers who went to discuss Fort Sumter's surrender accidentally drank from a bottle of poison (thinking it was whiskey) but Fort Sumter's surgeon saved his life with a stomach pump. And the only Union deaths were caused by one of their own cannon exploding as the US flag was lowered. Otherwise, Fort Sumter was a battle without casualties.
None of the Union defenders at Fort Sumter were killed by the Confederate barrage. The only deaths were because Captain Doubleday insisted on firing a cannon as the US flag was lowered, and the cannon exploded, killing two men.
Because Lincoln did not recognise the Confederacy, and declared that he would defend his small garrison at Fort Sumter.
Major Robert Anderson, US Army, was in command of the Federal garrison at Fort Sumter.
The Geography of the US.
The Confederate capture of Fort Sumter was important to the US Civil War because it was the event that led to the US Civil War.
The Southern state of Florida was the second US state to secede, not the third one. Before the bombardment of the Federal Fort Sumter in Charles harbor in April of 1861, seven states were part of the secession. Four others joined after the fall of Fort Sumter.
Fort Sumter in Charleston Harbour. The Union garrison evacuated the fort, and Lincoln called for new volunteer troops. This was the equivalent of declaring war. (There was, of course, no official declaration, since Congress did not recognise the Confederacy as a sovereign nation.) Fort Sumter, being the property of the US, was the first step to the US Civil War. Mr. Begg is correct that it was aftert Fort Sumter that the US Civil War began.
The Federal fort, Fort Sumter was located in the Charleston harbor in South Carolina. Southern forces attacked Fort Sumter, and the commander of the fort surrendered. This conflict led to US President Lincoln to ask for volunteers to serve for 3 months.