If there is no footnote or other reference, the person reading your paper assumes that the ideas are all yours. When you borrow an idea from someone else without giving that person credit, you are stealing the idea. This is called plagiarism.
Plagiarism is dishonest, a form of academic misconduct.
Click here to read it. There are standard formats to indicate that you are borrowing ideas from other sources, and these can be found in style manuals. Besides telling you how to write footnotes and bibliographies, style manuals also tell you what your margins should be, what should be on the title page of your paper, and lots of other good stuff about writing a research paper. A Guide for Authors, Editors, and Publishers in the Biological Sciences You can see that there are many kinds of style manuals, for different groups of people. Here at EMU, unless a professor specifies otherwise, you generally should follow the style as presented in Lester's Writing Research Papers .