How do I find out who has cited an article?

I want to know if any other articles use my article as a source.

Generally, the more times an article has been cited, the most important it is in the literature.

Many databases--including Scopus, Web of Science, and Google Scholar--tell you how many times an article has been cited by other articles in the database. You'll usually find this information in either the search results screen or in the detailed view of the article (examples below)

Not all databases have this feature. Also, this feature only tells you how many times the article has been cited within the database you're using. It won't be able to tell how many times the article has been cited in articles or books that aren't in that database.