Here's another example of words that are often confused.
In English, something that is popular is liked by many people. Examples: a popular song, a popular television show, a popular style of clothing. Remember: If people don't like it, it isn't popular.
Therefore, we don't normally talk about a popular disease, or a popular insect that eats all our vegetables. Instead, we use the word common, which means easy to find, not rare, something existing in great numbers, etc. (Sometimes things can be both common AND popular:)
There is another meaning of common--the opposite of noble. In this sense, it can also be used to mean vulgar.
The common people are not interested in your ancestors.
The princess mustn't marry that man--he's so common.
And if you and I are both interested in the same subject, or come from the same town, we have something in common.