It is important that you give credit to the people whose works contributed to your ideas. This is done by including a BIbliography or Works Cited page. It is critical to avoid plagiarism, and also a bibliography is useful providing other resources for someone else who is researching your topic, or an aspect of your topic.
There are different ways of citing your sources, depending on which style you are using. Your instructor should tell you which one to use. Each style has its own manual.
The best online source for APA and MLA styles is the OWL at Purdue.