If you've written an annotated bibliography, the easiest way to think about a literature review is that it's a step beyond that.
In an annotated bibliography, you identify sources on your topic and explain their relevance. In a literature review, you make connections between sources on the basis of a research question.
A literature review isn't quite the same thing as a research paper. In a research paper, you're making your own argument. In a literature review, you're providing background information about what previous scholars have said.
Plagiarism is using someone else's work -- their words or ideas -- without giving them credit. Even accidental plagiarism can have big consequences, so you want to be careful to avoid it.
Avoid plagiarism by documenting your sources as you do your research and writing. If you use a quotation or refer to an idea, be sure to keep track of where you found it so that you can cite it properly.