To avoid plagiarism, you must give proper credit to all sources you use! Whenever you paraphrase or directly quote information, you must cite the source of the information using a specific citation style.
Two common citation styles are APA (American Psychological Association) and MLA (Modern Language Association).
The citing help inside a research database is a good starting point, but ALWAYS check the references because the formatting is NOT 100% correct.
You can use citation generators like BibGuru to format citations, but they are not perfect, either. Double check your citations before submitting your work!
See the Purdue OWL for examples of citing sources properly: