Meals & nutrition

I recently finished building a small tool, and now I need to explain how it works. I know every part of it, but writing instructions that another person can follow is proving difficult. A friend suggested I hire technical content writer. Has anyone done this before? I am wondering what information a writer needs from someone who knows the technical side. Do you normally provide notes, demonstrations, or detailed instructions? Hearing how others started would make the process much easier for me to understand.