Citing sources is all about documenting whose ideas/facts you are using, where you found the information, and when the information was created. Within your paper or project, you will note when you're including a fact or idea that you found in your research, and at the end of your paper or project, you will list the detailed sources of that information.
Different assignments may require different citation formats. Your English teacher will probably ask for MLA Style, your Science teacher will most likely ask for APA Style, and your History teacher may ask for Chicago Style.
Regardless of which format you use, much of the basic information is the same. As long as you have the details about your sources, you will be able to cite them correctly.
Lucky for you, there are many tools available to assist you online.
Purdue University's Online Writing Lab (OWL) is one of the most comprehensive and reliable resources for doing research, writing papers, and citing sources.
Here's Purdue OWL's complete guide to citations:
Here's Purdue OWL's homepage with resources for teachers and students, Grades 7-12, ELLs, and more!