hi, welcome! hmm, i don’t think npm start is the right command, that is usually just for spinning up a server on localhost which is different than deploying your site to netlify. 
This Common Issue contains a ton of useful debugging tips that can likely help you solve your problem 
If you are still having problems, please provide as much information as you can on what you have already tried, what your build settings are, your package.json, etc. Thanks!