Students often ask about the difference. There is no real difference for the English language student. But the basic difference is an idiom uses words that do not have a direct meaning, like “it’s raining cats and dogs” but a proverb is a piece of advice like “an apple a day keeps the doctor away”.
Another point, proverbs are often based on religion, such as Buddhist (Chinese) or Christian Proverbs.
Here are a couple of link to use