The Afro-Cuban 'Conga' (Spanish=a Congolese woman) is really a "Mixer" type dance, done by a solo or group of dancers most common in a single file line. When done as a couple, the dancers face each other and move opposite direction of one measure, then switch directions on the next measure (1,2,3,* 1,2,3,*).
Couples can join hands and do patterns to this rhythm as well as turn. When done as a couple, hands are changed on the third beat. The Conga may be done touching or separate or as a mixture.
When done as a Conga Line, generally the person behind the next places their hands upon the front persons hips and this continues on down the line. The dance does not necessarily stay on the dance dance floor, it can and does zig-zag through out the room. The basic steps are (Left) 1-2-3-Kick (or Bump) then repeat, opposite. The Boomp-si-Doodle was often mixed with this dance. Originally a band member, wearing a drum and beating out a tune would venture onto the dance floor. He would start zig-zagging around the floor and tables playing his drum and the dancers would start to follow behind him doing the dance like a slithering snake all the while the line grows and the drums would intensify until the drum just stopped being played, no fancy ending.
The Conga is said to be brought from Africa by the Slaves to Cuba and the suger plantations of the West Indies which had been danced there for years. During the Machado dictatorship in Cuba, peasants were forbidden to dance the Conga because rival groups would work themselves to high excitement and explode into street fighting. Col. Fulgencio Batista, a political strong man of Cuba, relaxed the rules somewhat permitting Congas during election time but a police permit is required for public dancing of the Conga at all other times. Then it drifted onto Paris and was the sensation of 1936 in Montmartro and Montparnasse. The dance started to gain some popularity in the USA around 1929 when the original La Conga Nightclub (57th Street) opened it's doors (which later became La Martinique owned by Ramon and Dario.) By 1937, the Conga was all the rage in New York.
Desi Arnaz (aka Ricki Ricardo of "I Love Lucy") is credited with making the Brazilian Conga popular here in the United States and became popular around 1939. Many night clubs would advertise "Conga Night or Conga Room" which was another term for Latin American Music that would be played. However the Conga Line was done much earlier and was introduced at a wedding Reception (Frieda's) as early as 1905 by the "Gloriosky Old Maids", specifically Prudence Adams.
... As a side note the dance Balboa and Conga share the same rhythm 1-2-3-kick-1-2-3-kick. (Yes, I know that Bal has other rhythms as well.) Just an interesting observation that I thought I'd share lol. In the soundie clip "Swing Cats Jamboree" at the end of the film is a dance scene with the kids doing a kinda fast Bal-Conga couples dance to big band music buy Louis Prima.