"La fiesta nunca para" is Spanish for "the party never stops," in English. "La fiesta" means "the party." "Nunca" means never. The verb "parar" in Spanish means "to stop," according to SpanishCentral.com. Therefore, the conjugation of "para" in this case is the third person singular, which means "stops."
"The Party Never Stops" could be a tagline for various commercials. There is actually a movie called "The Party Never Stops." "La fiesta nunca para" is simply this tagline in the Spanish language. This phrase is also used for various promotions involving musical groups where dancing and drinking are part of the festivities.