Claiming another person's research or another person's idea as your own is known as plagiarism. The minimum punishment for plagiarism is a failing grade for the paper, or could result in failing the course itself.
Quoting or citing other people's ideas does not weaken your paper. In fact, it strengthens your arguments and can help you get a better grade. If you are in doubt about when to cite, talk to your course leader or to the staff at the library. They can give you advice on when to cite another source.
There are three internationally accepted styles of citation: Harvard, Chicago and MLA. Different areas of study use different methods of ciation. Talk to your course leader or a librarian if you have any questions.
For your convenience, we provide this guide (pdf) to writing citations based on the MLA style of reference.