Why should you cite your sources?
There are many different styles of citation. Always ask your teachers which citation style they prefer.
These are the three most popular styles:
APA (American Psychological Association): Often used in the social sciences, e.g. psychology, education, anthropology
MLA (Modern Language Association): Often used in liberal arts and humanities, e.g. English
Chicago Manual of Style: Common in history, but sometimes used in other social sciences.
Your teacher may use a variation of one of the above styles or may use their own - it is usually stated in the assignment. When in doubt, ask the teacher!