You can find a boilerplate mutual NDA online pretty easily. The real valuable advice here is that these are far less necessary than most first time founders are led to believe.

If you are going to engage with someone on a deep level and share with them proprietary data and highly valuable company secrets, and they are very motivated to work with you, an NDA is fine. However, many first time founders run around afraid to share their idea with people unless they have an NDA in place. They also reach out to people for advice, mentoring, help with something, asking for a favor from someone, and then ask that person to sign an NDA. It's very bad form.

99.99999% of the time, nobody is going to steal your idea or do anything with the information you share. You're lucky if you can get people to care at all, let alone steal your idea. You are far more likely to get lots of help and benefits by sharing your story freely than you are to get screwed by someone who takes your idea and has the desire, time, resources, talent and perseverance to build your startup faster than you.

The reason why your idea seems so valuable early on is because it's all you have and you worry about someone taking it and executing faster than you. Most people already have ideas of their own that they're not doing anything with. The minute you start building your company you realize that the idea was the easy part and it's the everyday grind that is hard. At some point, you start to wish people would try to copy you because it will be funny to watch them struggle as you have.

You can get a standard NDA by searching online or just asking a company you're friendly with to send you theirs. Chances are, usually, you don't need one.