A idol is usually a statue which could be made out of gold, or other expensive materials. In ancient times, (and are somewhat still used today) Idols were worshipped like gods. An example of an idol is the "golden calf," in Judiasm while the Jewish people were waiting for moses to come down from Mount Siani and have them receive the Torah they "lost faith" in god and melted a gold idol into the shape of a calf and worshipped it. This was a sin.
A hero is a living thing that helps solve a problem. if you think about it a hero can be big or small. A "Big" hero can be someone who helped for example, save the man before the sharks can attack him. A small hero can be someone that lends you a pencil in class because you don't have any and if you aren't prepared you could get detention.
I hope this helps.
