You need to cite your source any time you use the exact words of another source, or any time you paraphrase, summarize, or refer to ideas, information, or facts you draw from that source that are not common knowledge.
Citing sources is important as:
Quotation means using the exact words of the source you are quoting. You should not change anything or leave anything out.
Use quotations when the author's wording or phrasing is particularly effective or powerful, and you want to include it in your paper. Quotations are also useful when the exact wording of a source is important for other reasons.
Quoting, Paraphrasing, and Summarizing--The Purdue Owl
A summary is a short passage of writing that explains very briefly the key ideas or most important information from a much longer passage of writing. A summary can be simply a sentence that describes the key ideas of a paragraph, or a few sentences that sum up an entire book or article.
Summaries are always written in your own words; if their wording is too similar to wording from the source they are summarizing, it's plagiarism. Always make sure you are restating the idea in your own words.
Use a summary when what matters is the most important idea or ideas from the work you are citing.
A paraphrase is restating an idea or fact in your own words, in a passage of similar length to the one you are restating. If the original work is a sentence or two, your paraphrase should also e a sentence or two.
You should avoid paraphrasing long passages; if you need to refer to or borrow an idea from a passage that's longer than a few sentences, you really should summarize instead of paraphrase.
The paraphrase must be written in your own words, and must accurately restate the idea you are referring to. If your wording is close to the originals, it's plagiarism. If your wording changes the meaning of the idea you are referring to, you are misrepresenting the author.
(California State University, Long Beach, 2021)
Some facts are widely known, and are not disputed by anyone, and so do not need to be cited.
For example, Abraham Lincoln was the 16th President of the United States does not need a citation. It is common knowledge; it can be easily looked up or verified in any relevant reference book, and there is no debate or controversy over it.
William Seward was Abraham Lincoln's Secretary of State and was injured by a conspirator the same night Lincoln was killed does need a citation. While it can be easily verified, it is not common knowledge; most people don't know it.
Abraham Lincoln was the first homosexual President of the United States also would need a citation, because it is a very controversial claim, and your reader will want to know where you got that idea. Many historians would dispute it, so if you include it you must show where you got it.
Not everything that can be looked up is common knowledge. If different sources disagree, even slightly, you need to cite your source for a fact even if it can be looked up. For example, different sources will give a different population for the town of Toppenish. If the information you are referring to is technical or specialized, you should cite it. Common knowledge refers to things that just about everyone knows and that there is no real debate over the truth or accuracy of. Use your judgement.
Common knowledge depends on who your audience is. Doctors writing for other doctors, for example, often will not cite sources for the symptoms of the disease they are writing about, assuming that this information is common knowledge for their audience. Likewise, if you were writing for a non-American audience, you might cite the statement Abraham Lincoln was the 16th President of the United States, since this can only be assumed to be common knowledge for an American reader.