Cumbia — the Colombian coastal groove that became the common dance music of Latin America. The guacharaca (a ridged scraper, here the shaker voice) plays the signature "chk · chk-chk": a long scrape on each beat and two short ones on the "and" and the "a" after it. Under it the llamador drum keeps 2 and 4 (conga-lo) and the alegre answers on every off-beat (conga-hi); a kick marks 1 and 3.
The chord instrument — accordion in vallenato, piano or guitar in a dance band — plays short chords on every "and", never on the beat, like a faster, bouncier skank; the bass holds the floor with root on 1, a pushed fifth on the "and" of 2, root on 3 and fifth on 4.
Listen for the scraper: its "long-short-short" is the thing people clap along to. Mute it and the off-beat chords sound like reggae; add it back and they become cumbia. Practice: tap the long-short-short with one hand and the off-beat chords with the other before you play either part.