When using sources in your papers, you can avoid plagiarism by knowing what must be documented.
Specific words and phrases
If you use an author's specific word or words, you must place those words within quotation marks and you must credit the source.
Information and Ideas
Even if you use your own words, if you obtained the information or ideas you are presenting from a source, you must document the source.
Information: If a piece of information isn't common knowledge (see below), you need to provide a source.
Ideas: An author's ideas may include not only points made and conclusions drawn, but, for instance, a specific method or theory, the arrangement of material, or a list of steps in a process or characteristics of a medical condition. If a source provided any of these, you need to acknowledge the source.
You do not need to cite a source for material considered common knowledge:
General common knowledge is factual information considered to be
in the public domain, such as birth and death dates of well-known figures, and generally accepted dates of military, political, literary, and other historical events. In general, factual information contained in multiple standard reference works can usually be considered to be in the public domain.
Field-specific common knowledge is "common" only within a particular field or specialty. It may include facts, theories, or methods that are familiar to readers within that discipline. For instance, you may not need to cite a reference to Piaget's developmental stages in a paper for an education class or give a source for your description of a commonly used method in a biology report—but you must be sure that this information is so widely known within that field that it will be shared by your readers.
If in doubt, be cautious and cite the source. And in the case of both general and field-specific common knowledge, if you use the exact words of the reference source, you must use quotation marks and credit the source.