A proverb is a well-known phrase that gives advice or says something that is generally true.
Proverbs are fixed groups of words so you can't change the wording of a proverb. For example you can say "Too many cooks spoil the broth" (a lot of people will make a mess of trying to complete a task together) but you can't say "Too many cooks spoil the soup".
Proverbs are also so well-known that we often only say the first half of them (the rest we leave unsaid because everyone knows the ending). So for example, Tim said "A fool and her money.." when the whole proverb is "A fool and his money are soon parted" which means that stupid people find it difficult to hold on to their money.
In the examples below the part in brackets is often left unsaid.