Charleston is often called "the grandfather of swing." Lindy Hop, which is the original swing dance, came out of Charleston. The charleston step is still a part of Lindy Hop, but as a dance, Charleston predates Lindy Hop by about 20 years. Charleston itself came out of another dance called the Cakewalk, which was created by African-American slaves as a way of making fun of the dances done by their white owners.
It's hard to tell exactly when Charleston got started, but it is usually dated around 1903. It was made popular in 1922 by the Broadway play Runnin' Wild and became a national dance craze. Just about everyone danced Charleston. Being good at Charleston was considered fundamental to being able to teach dance of any kind. It was eventually replaced by Lindy Hop, but it remains a step in Lindy Hop.
There are many variations of Charleston, including side-by-side Charleston, tandem Charleston, front-to-front Charleston, 20s Charleston, and flying Charleston. Charleston can be done as a solo dance, a partnered dance, or a line dance. Side-by-side Charleston is probably the most basic form. The follower stands to the right of the lead, who puts his right arm around her, and the follower mirrors the lead's movements. It is an eight-count dance, and the leader's steps are rockstep on the left foot, kick and step forward with the left foot, kick forward with the right foot, then kick and step backwards with the right foot.