Intentional plagiarism is, as the name implies, a willful attempt on the part of a student to commit academic fraud in a written work. Examples of intentional plagiarism would include cutting and pasting text from a website without proper attribution, copying text from a printed source without proper attribution, submitting another student's paper as your own for an assignment or re-submitting work that you did for another class to fulfill an assignment.
Students commit unintentional plagiarism when they are unaware of an institution's plagiarism policies, are unaware of the proper citation conventions necessary for writing a paper or are aware of the conventions, but accidentally forget to cite a source properly due to carelessness. For example, some instructors may construe Hacker's definition of plagiarism as leaving out quotation marks around ideas and quotations taken from a source as unintentional plagiarism due to carelessness or sloppiness. You should be aware, however, that institutions still view unintentional plagiarism as an offense and may punish you accordingly.
Receiving feedback on any written work, whether or not that work involves research, is always beneficial, so you can improve your writing skills. However, you may be afraid to seek out writing tutoring or feedback from other knowledgeable peers due to the fear of being accused of plagiarizing ideas. Incorporating peer and tutor feedback into your writing is not plagiarism so long as you use your own words to integrate their ideas into your work. If you are worried about whether seeking peer or tutor feedback constitutes plagiarism, be up front with your instructor, discuss the nature of the feedback and, if possible, secure written documentation from your writing tutor if you have worked with one.
One way to avoid plagiarism is to read your research source, close it and set it aside and then try to write out ideas from the reading in your own words without referring to the source material itself. After you have incorporated information into your paper, you can go back and look up appropriate page numbers and citations. Another effective way to avoid plagiarism is to ask your instructor, a tutor or a knowledgeable peer to read your research paper while it is still in the draft stage and discuss with them how you are using sources to support your argument. If your school subscribes to plagiarism prevention software, you may be able to check your paper for plagiarism while it is still in the draft stage depending upon how your instructor has configured the software settings for your course.
Before writing a paper for any course, you should familiarize yourself with your school's plagiarism policies and punishments, as ignorance of these policies will not suffice as a defense in a case of intentional or unintentional plagiarism. When in doubt as to whether you should cite a source in a paper, err on the side of caution and cite the source. In addition, don't be afraid to talk to your instructor if you have a question about the appropriate use of sources in a paper. By talking to your instructor about your concerns, she will know that you are making your best attempt to avoid plagiarism.