Whenever you use another person's ideas or words, you must give them credit. You do this by CITING the source you used in two places:
Citing your sources properly shows that you have done your research and consulted appropriate sources for your topic. It also acknowledges that all research builds on work that has come before. You are giving credit to sources that have influenced or informed your work. If you do not do this, you are essentially stealing another person's ideas, which is plagiarism.
Different scholarly disciplines follow different 'rules' to format citations. For ARTS 1100, you will be using the APA citation style.