Using the computer to copy and paste is probably the most common way students inadvertently plagiarize.
Here's how to avoid plagiarism when you copy/paste text FROM ANY SOURCE:
Your instructor will let you know which style (APA, MLA, or Turabian) to use for your paper.
In addition to in-text citations, you need a bibliography (References / Works Cited) that lists each source cited in-text.
If you interview someone without identifying your source, even if it is a casual conversation from which you get ideas and/or quotes, it is plagiarism. You must cite your source.