Citing is different from but related to plagiarism. When you use other people’s words or ideas you need to credit them, and so you “cite” them. By including that citation you will avoid the charge of plagiarism.
Unfortunately, you cannot just cite your sources in a haphazard or idiosyncratic way. There are rules you have to follow. The manuals, or “rule books” are called Citation, or Style Guides. The Style Guide will give you explicit directions on format, capitalization, punctuation, spacing, etc. You need to provide both in-text citations and references/bibliographies list in the end of your paper according to the citation style required or of your choice.
There are several main Citation Style Guides used in the academic world. Here are some links to citation style guides.