Buttons vs links

I was wondering what is the proper usage for a button and a link when building an accessible application or website?

I'm reading multiple articles on this topic and I read an article from the Nielsen Norman Group on command links and they state that buttons should not be used for navigation and that users should click a plain link to move to another page of information. Multiple articles I have read  on using buttons and links when creating an accessible application or page mention this too.

Article: Command Links<https://www.nngroup.com/articles/command-links/>

Thank you in advance,

Angela Savage
Accessibility Auditor