If an idea wasn't yours, you should cite it in-text.  This includes:

• Direct quotations
• Paraphrasing (putting someone else's ideas into your own words)
• Using an idea that someone else gave you in a conversation, email, class, etc.
• Describing an idea that influenced your work
• Expert opinion or lending authority to your own opinion
• Giving any information that isn't common knowledge
• Using any or all of a previously created work of your own design (yes: self-plagiarism is a real thing)