Any words, ideas or images that you do not create yourself must be properly credited to avoid plagiarism.
Citing information sources acknowledges the origin of your information and it provides support and credibility to your work by showing evidence of your research.
A citation is a reference to the source of an idea, information or image. It typically includes enough identifying information, such as the author, title, date, publication format, etc.
Monash University citing and referencing: Vancouver Style
More about citing sources.