What is the difference between myth and legend?

I was thinking I should set some things clear at the beginning; before I set to fulfil my challenge.
Myths and legends seem to be the same things but they differ slightly.

I did a little research and found out that legends are the stories based on the true event from the past which have been passed through generations. There usually is a real hero. On the other hand, myths are stories created by people in order to teach or explain certain facts or events (such as natural disasters or religious questions).
There are also folktales - stories passed from one generation to the next in the spoken form.

I am interested here in all these forms (and more). I'm setting off with Greek and Roman myths, then moving on to polish legends and folktales. Strange combination, I know, but this is what I currently have on my bookshelves. The collection will hopefully expand and I will be able to ponder on the stories from other regions,too. Any suggestions are welcome.

The challenge starts here!