Here's an example:
High-Dose Daptomycin for Treatment of Complicated Gram-Positive Infections: A Large, Multicenter, Retrospective Study
Ravina Kullar, Susan L Davis, Donald P Levine, Jing J Zhao, Christopher W Crank, John Segreti, George Sakoulas, Sara E Cosgrove and Michael J Rybak
If you are one of those names following the title, you are an author. If you appear in a section stating "The authors gratefully acknowledge the contributions of Student X and Post-Doc Y", then you are not an author, regardless of how much you actually contributed.
If you do not appear in the author section, then you may not put the paper down as a publication. You can mention it as pertinent research experience (if it was in fact research that you were doing), but you did not author a paper.