Complex sentence: Dressed as friendly farmers or civilians in the daytime, they took part in guerrilla activities at night: ambushing small detachments of American soldiers, sabotage, and most importantly, supplying Abad with intelligence on American positions and movements.
Split into simpler sentences: Dressed as friendly farmers or civilians in the day time, they took part in guerilla activities at night. Ambushing small detachments of American soldiers, sabotage, and most importantly, supplying Abad with intelligence on American positions and movements.