ECO mode can be used when there is repeated braking while you drive, eg when you are driving through the city. it reduces the acceleration and air conditioning, air conditioning can be manually adjusted later.
EV mode can be used if you want to drive your car solely on electric power. if battery is full and you press EV mode,it will give you a drive of 2 km on battery,provided your stay within the speed range. Nothing special in this mode..
read this information in owner manual of prius c,the variant of aqua...