The difference between them is that acrylic is very opaque, fast drying, and they usually can be diluted with water but become water resistant when dry. watercolors are very thin that you can almost see through them. and acrylic paint is very predictable while watercolors aren't. when using watercolors, you usually just let the paint do the work. Hope that helped? :)
Acrylics are based on a water-soluble plastic, while watercolor are just water based. There are cheaper and more expensive versions of each type of paint. Watercolor is generally used on paper while acrylic is generally used on canvas.