Traditional citation information can serve numerous purposes from showing the impact of an authors' published works to providing information on the scholarly journals publishing these articles.
Many of the library databases provide information on the number of times an item indexed in them have been cited by the other items within that particular database as well as providing information on the citing articles.
Some databases such as the Scopus database from Elsevier have the ability to directly search for cited articles regardless as to whether the journal containing the article is indexed in the database. In other words, this will show whether any of the journals indexed in the Scopus database have included citations to an article even if the journal the article is published in is not indexed by Scopus.
The Scopus Database will also provide data on h-index (the value as well as a graphical representation), a citation overview, and an analysis of the author's output. It also provides information on the journals indexed within the database including their metrics of SCImago Journal Rank (SJR), Impact per publication (IPP), and Source normalized Impact per paper (SNIP). For more information on Scopus Journal Metrics -- https://www.journalmetrics.com/
Google Scholar also provides citation information for published articles. Just search for the article and click on the Cited by link. You should also probably review the Version link, if provided to ensure you have the correct version of the article.
Consult with your subject/departmental library liaison as to which subject specific databases provide citation information and how to search for this type of information.