Plagiarism is using ideas or the work of another person and presenting it as your own work. It is dishonest, unprofessional and poor scholarship. Examples of this might include cutting and pasting work or closely paraphrasing another’s ideas, writing or design. Collusion is a form of plagiarism where two or more people work together to produce a piece of work but where all or part of the work is submitted as their own work. Group work where students are encouraged to work together to produce a single piece of work for assessment is not collusion. Plagiarism is a form of cheating.
Plagiarism - A Link to a comprehensive plagiarism Libguide
You might want to consider using reference management software to help you with your referencing. There are several options available including Endnote, Endnote web, Mendeley, Zotero and others.
For more information on zotero: https://libguides.wits.ac.za/zotero
Giving credit to the original author by citing sources is the only way to use other people's work without plagiarizing. But there are a number of other reasons to cite sources:
From Plagiarism.org