In school, the penalties for plagiarism can range from an F on the assignment to an F in the course, or even expulsion from school. If your plagiarism ends up on your academic record, it will follow you for the rest of your life. Other schools may not admit you, and employers will think twice about someone whose academic honesty is so tarnished.
In life outside of school, plagiarism is still a big deal. Do a Google News search on Plagiarism to see. Authors, politicians, and others get caught regularly. An accusation of plagiarism, especially when proven true, can be a career and reputation destroyer. Plagiarism leads others to doubt a person's honesty, ethics, and overall character.
The following links will take you to some more tips on avoiding plagiarism:
Editage. Tips to Avoid Accidental Plagiarism. YouTube.