'Citation Tracing' (also known as 'Citation Tracking') refers to both finding references cited in a given article and finding newer articles that cite the original article. This allows you to follow research through time--cited references are past research, while citing works are more recent (relative to the article you already know about.)
Cited References ->
Known Article ->
To find a reference, or any known article in Google Scholar, enter the article title into Google Scholar. If the article doesn't appear in the first few results, try putting quotation marks around the entire title or key phrases and/or adding an author's lastname.
In the Results list of Google Scholar, below the entry for each result that has been cited, will be a 'Cited by [number]' link. The [number] is how many other entries Google Scholar has found that cite that work. Some of these may be duplicates. Click the link to see a list of citing works.
If there is no 'Cited by' link, then Google Scholar has not found any citing works. That does not mean it hasn't been cited, just that GS doesn't have records.
Note: pay attention to dates. Extremely new articles will have few if any 'Cited by' works, just because no one has had time to publish anything newer. Classic and high impact works may have hundreds (even thousands) of 'Cited by' works.