An NDA and a patent are two very different things. A patent is something that legally gives you full rights over an idea or a product and protects your idea as your own. This prevents others from claiming your idea as their own and suing you for using it. An NDA, or non-disclosure agreement, is something that is signed by all those involved in the project that restricts them from talking about it. For example, if you are unhappy at your current company and would rather work at another one, an NDA would prevent you from taking a recent idea that you signed an agreement for and bringing the details of it to the next company, preventing them from working on a similar/the same product. While it may not protect your idea and give you ownership of it like a patent does, an NDA is a helpful tool that prevents ideas from being leaked to rival companies.