A citation is just a recipe that lets anyone find the exact source you used. Every style includes the same ingredients — who wrote it, when, what it's called, where it appeared, and a link (usually a DOI). The styles only differ in the order and punctuation. Here's how the three most common ones handle a journal article.
What a DOI is
A DOI (Digital Object Identifier) is a permanent address for a paper, like 10.1038/s41586-020-2649-2. Unlike a normal URL, it never breaks — https://doi.org/ plus the DOI always resolves to the current location of the paper. Include it in every citation when one exists.
APA (7th edition)
Author, A. A., & Author, B. B. (Year). Title of the article. Journal Name, Volume(Issue), pages. https://doi.org/xxxxx
Example: Doudna, J. A., & Charpentier, E. (2014). The new frontier of genome engineering with CRISPR-Cas9. Science, 346(6213), 1258096. https://doi.org/10.1126/science.1258096
MLA (9th edition)
Author Last, First. “Title of the Article.” Journal Name, vol. #, no. #, Year, pages. DOI.
Example: Doudna, Jennifer A., and Emmanuelle Charpentier. “The New Frontier of Genome Engineering with CRISPR-Cas9.” Science, vol. 346, no. 6213, 2014, https://doi.org/10.1126/science.1258096.
Chicago (notes-bibliography)
Author Last, First. “Title of the Article.” Journal Name Volume, no. Issue (Year): pages. DOI.
Example: Doudna, Jennifer A., and Emmanuelle Charpentier. “The New Frontier of Genome Engineering with CRISPR-Cas9.” Science 346, no. 6213 (2014): 1258096. https://doi.org/10.1126/science.1258096.
In-text vs. the reference list
The full citation above goes in your reference list at the end. In the body of your text you use a short pointer: (Doudna & Charpentier, 2014) in APA, (Doudna and Charpentier) in MLA, or a footnote number in Chicago's notes style. Every in-text citation must have a matching full entry, and vice versa.
Let a reference manager do it
For anything longer than a couple of sources, use a reference manager like Zotero, Mendeley or EndNote. You import a paper once (as BibTeX or RIS) and the tool formats it in any style and builds your bibliography automatically — no manual punctuation-wrangling.
In PaperFinder, hit “Cite” on any result to copy a ready-made APA, MLA, Chicago, BibTeX or RIS citation, or select several papers in My Library and export them all as BibTeX/RIS to drop straight into Zotero or Mendeley.