I'm really struggling with my software specs. I am not a professional programmer but enjoy doing it for fun and made some software that I want to sell later but I'm not happy with the code quality. So I wanted to hire a real developer to rewrite my software in a more professional way so it will be maintainable by other developers in the future.

I read and found some sample specs and made my own by applying their structure to my document and wanted to get my developer friend to read it and give me advice. After an hour and a half he understood exactly what I was trying to do and how I did it(my algorithms,stack,etc.).

How can I get better at explaining things to developers? I add many details and explanations for everything(including working code) but I'm unsure the best way I can learn to pass detailed domain knowledge(my software applies big data, machine learning, graph theory to finance). My end goal is to get them to understand as much as possible from the document and then ask anything they do not understand, but right now it seems they need to extract alot of information from me. How can I get better at communicating domain knowledge to developers?