It goes by many names. Whether you call it Emancipation Day, Freedom Day or the country's second Independence Day, Juneteenth is one of the most important anniversaries in our nation's history.

On June 19, 1865, Maj. Gen. Gordon Granger, who had fought for the Union, led a force of soldiers to Galveston, Texas, to deliver a very important message: The war was finally over, the Union had won, and it now had the manpower to enforce the end of slavery.

The announcement came two months after the effective conclusion of the Civil War, and even longer since President Abraham Lincoln had first signed the Emancipation Proclamation, but many enslaved Black people in Texas still weren't free, even after that day.

That was 156 years ago. Here are the basics of Juneteenth that everyone should know.

First things first: Juneteenth gets its name from combining "June" and "nineteenth," the day that Granger arrived in Galveston, bearing a message of freedom for the slaves there.

Upon his arrival, he read out General Order No. 3, informing the residents that slavery would no longer be tolerated and that all slaves were now free and would henceforth be treated as hired workers if they chose to remain on the plantations, according to the National Museum of African American History and Culture.

"The people of Texas are informed that in accordance with a Proclamation from the Executive of the United States, all slaves are free. This involves an absolute equality of rights and rights of property between former masters and slaves, and the connection heretofore existing between them becomes that between employer and hired laborer," the order reads, in part.

It's perhaps unsurprising that many former slaves did not stay on the plantations as workers and instead left in search of new beginnings or to find family members who had been sold away.

"It immediately changed the game for 250,000 people," Shane Bolles Walsh, a lecturer with the University of Maryland's African American Studies Department, told NPR.

Enslaved Black people, now free, had ample cause to celebrate. As Felix Haywood, a former slave, recalled: "Everybody went wild. We all felt like heroes ... just like that, we were free."

When Granger arrived in Galveston, there still existed around 250,000 slaves and they were not all freed immediately, or even soon. It was not uncommon for slave owners, unwilling to give up free labor, to refuse to release their slaves until forced to, in person, by a representative of the government, historian Henry Louis Gates Jr. wrote. Some would wait until one final harvest was complete, and some would just outright refuse to submit. It was a perilous time for Black people, and some former slaves who were freed or attempted to get free were attacked and killed.

For Confederate states like Texas, even before Juneteenth, there existed a "desire to hold on to that system as long as they could," Walsh explained to NPR.

Before the reading of General Order No. 3, many slave owners in Confederate states simply chose not to tell their slaves about the Emancipation Proclamation and did not honor it. They got away with it because, before winning the war, Union soldiers were largely unable to enforce the Emancipation Proclamation in Southern states. Still, even though slavery in America would not truly come to an end until the ratification of the 13th Amendment, the Emancipation Proclamation still played a pivotal role in that process, historian Lonnie Bunch told NPR in 2013.

"What the Emancipation Proclamation does that's so important is it begins a creeping process of emancipation where the federal government is now finally taking firm stands to say slavery is wrong and it must end," Bunch said.