You follow the rules of your citation style of choice, e.g. in APA something like
Roy Rosenzweig Center for History and New Media. (2016) Zotero [Computer software]. Retrieved from www.zotero.org/download
APA wants you to cite the version number in text. In other styles you'd include it in the citation (which I'd consider better practice). If you're writing about the code rather than the tool, you could consider citing the github repository and possibly even relevant commits, but that doesn't seem relevant here.
Generally, I don't think it's customary or necessary to cite Zotero if you've used it as a reference manager any more than you'd cite Word. If you write about Zotero or if you use it to collect or analyze data, some version of the above.
This probably should be on the about Zotero page. While citing software is easy, figuring out the (institutional) author is not trivial in the case of Zotero (e.g. the About page makes it seem like joint authorship between the Roy Rosenzweig Center and the Center for Digital Scholarship, but the citation above has only the former).
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Roy Rosenzweig Center for History and New Media. (2016) Zotero [Computer software]. Retrieved from www.zotero.org/download
APA wants you to cite the version number in text. In other styles you'd include it in the citation (which I'd consider better practice). If you're writing about the code rather than the tool, you could consider citing the github repository and possibly even relevant commits, but that doesn't seem relevant here.
Generally, I don't think it's customary or necessary to cite Zotero if you've used it as a reference manager any more than you'd cite Word. If you write about Zotero or if you use it to collect or analyze data, some version of the above.
https://forums.zotero.org/discussion/12698/cite-zotero-as-computer-program-with-zotero
https://forums.zotero.org/discussion/12773/bibliographic-reference-info-for-zotero-itself