Wikipedia:Training/Newcomers/Copyright and plagiarism
Wikipedia Training
Principles
Copyright and plagiarism
Although the importance of copyright and plagiarism issues may vary by country, Wikipedians working on the English Wikipedia take copyright issues very seriously.
In short, don't cut and paste content from other places into Wikipedia, even on sandbox pages. If you're paraphrasing a source, be careful to fully rewrite it in your own words. Avoid "close paraphrasing" that essentially copies the structure of the source and simply rewords it phrase by phrase.