Complex sentence: While walking around on the resort grounds, Baby encounters Johnny's cousin Billy and when Baby helps Billy carry watermelons to the staff quarters, she observes their secret after-hours party and the "dirty dancing" (i.e., the rock'n'roll) involved.
Split into simpler sentences: While walking around on the resort grounds, Baby encounters Johnny's cousin Billy and helps Billy carry watermelons to the staff quarters. There, she observes their secret after-hours party and the "dirty dancing" (i.e., the rock'n'roll) involved.