Paper ending: conclusion vs. conclusions
According to the Little, Brown Compact Handbook, in MLA style the final section is called the "Conclusion", while in APA style the final section will be labeled "Discussion". When using either citation style (and I would assume this holds no matter what citation style you are using), this section will contain your summary/interpretation, the conclusions (plural) that you wish the reader to take away from the paper, and perhaps a call to action or an outline of future work. So you are right, 


  conclusions [are] things to take away from a paper, and a conclusion [is] the end of something...


though not necessarily the end of a book; a conclusion can be the end of a paper, article, etc.