Researchers often like to see how many people have cited an article in the time since it has been published. Doing so helps you see how influential the research has been, and it can also help you find more current research on a given topic. Or maybe *you* have written an article, and you want to see who else is building upon your research.
Figuring out who has cited an article in Google Scholar is simple. First, perform a search. If you are looking for a specific article, put the title of the article in quotes.
Under each article, there should be a link that says "Cited by..." This is the number of articles in Google Scholar that link to the one you just found. Click on that number and you will be taken to a list of those articles.