Short answers, pulled from the story.
The Emancipation Proclamation, officially Proclamation 95, was a presidential proclamation and executive order issued by President Abraham Lincoln on the 1st of January 1863, during the American Civil War. It changed the legal status of more than 3.5 million enslaved African Americans in the Confederate states from enslaved to free.
The Proclamation applied to the ten Confederate states still in rebellion on the 1st of January 1863: South Carolina, Mississippi, Florida, Alabama, Georgia, Louisiana, Texas, Virginia, Arkansas, and North Carolina. Tennessee was excluded because it was already under Union military control, and the four slaveholding border states that remained in the Union, Maryland, Delaware, Missouri, and Kentucky, were not named.
Around 25,000 to 75,000 enslaved people were freed immediately in Confederate regions already under U.S. Army control. One contemporary estimate placed those freed on the 1st of January 1863 at roughly 20,000, covering Union-occupied areas of North Carolina and the Sea Islands of South Carolina. As Union forces advanced, the Proclamation provided the legal framework for the liberation of more than three and a half million enslaved people by the end of the war.
Lincoln issued the Proclamation under his authority as Commander-in-Chief of the Army and Navy, granted by Article II, Section 2 of the Constitution, framing emancipation as "a fit and necessary war measure for suppressing said rebellion." Because it was not a statute or constitutional amendment, Lincoln or a subsequent president could in theory have revoked it, which is why Lincoln also pushed for the Thirteenth Amendment.
The Proclamation turned foreign popular opinion toward the Union by making support for the Confederacy inseparable from support for slavery. This ended Confederate hopes of gaining official recognition from Britain or France. Henry Adams wrote that the Proclamation had done more for the Union than all its previous military victories and all its diplomacy combined. Giuseppe Garibaldi wrote to Lincoln on the 6th of August, 1863, predicting posterity would call him "the great emancipator."
Because the Proclamation was a war measure and not a permanent constitutional change, abolitionists worried it could be reversed when the war ended. Lincoln staked a major part of his 1864 presidential campaign on a constitutional amendment to abolish slavery nationwide. The Senate passed the Thirteenth Amendment on the 8th of April, 1864; the House on the 31st of January, 1865; and ratification by three-fourths of the states was completed on the 6th of December, 1865.