When you use somebody else's intellectual property - that is, any words, ideas, or images that you do not create yourself - you will need to give credit to the owner of said intellectual property. For research purposes we call this citing your sources.
When you cite your sources, you acknowledge the origin of the information. This lends credibility to your work by exhibiting evidence of your research and demonstrates the authenticity of your information sources. Your citations should be thorough enough that the reader can locate the same information you used in your research.