A citation is a way of letting your reader know that certain material in your work is from another source. The information that you include in the citation serves as an address for where the reader can find the source you used.
You can see examples in the guides linked above.
According to Boston University, "...every time you incorporate research, words, ideas, data, or information that is not your own", you need to give credit to the original source through a citation.This applies to summaries, paraphrases, and images too. ("When to Cite")
"Presenting work or ideas from another source as your own, with or without consent of the original author, by incorporating it into your work without full acknowledgement. All published and unpublished material, whether in manuscript, printed or electronic form, is covered under this definition, as is the use of material generated wholly or in part through use of artificial intelligence" ("Plagiarism").
Works Cited
“Plagiarism.” University of Oxford, University of Oxford, 2023, https://www.ox.ac.uk/students/academic/guidance/skills/plagiarism.
“When to Cite.” BU School of Public Health, Boston University, 2021, https://www.bu.edu/sph/students/student-services/student-resources/academic-support/communication-resources/when-to-cite/#:~:text=You%20must%20cite%20the%20source,that%20is%20not%20your%20own.