Generally, all the authors of a paper should be able to explain the research that was done from start to finish. All authors should have contributed to the research and/or the paper in a significant way. All authors will be accountable for the content of the paper.
The order of names varies in different disciplines. In the life sciences, the person who contributed the most significantly to the paper is often first and the PI is listed last. In organic chemistry, the PI is often listed first. In mathematics and physics, authors are often listed in alphabetical order.
Talk to your research group and collaborators about how you all want to handle authorship on writings that come out of your research early on. If you're working in a lab at an institution, you may want to ask someone what the norms are there.
Lead author - person who provided significantly to the research, though not always the PI or project lead. This person is often also the corresponding author.
Corresponding author - this is the person who submits the article to be published and works directly with the publisher. All inquires about the paper and the research will be handled by this person.
Coauthor - all coauthors should have contributed significantly to the research and/or the resulting paper.
Guest author - someone who didn't contribute directly to the research or the paper but to whom the authors want to give appreciate or respect. This is not common practice and best to be avoided.
The acknowledgements section notes funding agencies as well as organizations, groups, or individuals who supported the research and writing process but in ways that don't warrent authorship.
Content from this page was influenced greatly by the following titles, available at Temple Library.
The Craft of Scientific Communication by 
Clear and Concise Communications for Scientists and Engineers by 
