If your syllabus just says "cite your sources" without naming a style, the subject usually tells you which one to use.
APA — used in the social and natural sciences
Psychology, education, nursing, and business classes usually want APA. In-text citations look like (Smith, 2024), and the reference list is titled "References."
MLA — used in the humanities
English, history, and philosophy classes usually want MLA. In-text citations look like (Smith 124) — page number, no year — and the list is titled "Works Cited."
When in doubt
Ask your instructor, or check your program's writing center guide. Getting the style right is worth more than it seems: it is often graded separately from your content.