Step 1: Create a NPM account
In order to release your packge on NPM you need to create an account. Be aware that the email you expose there is going to be publicly visible.
Step 2: Prepare your package for release
In your package repo, run
npm init and fill out everything you're asked for. That makes sure your package is ready for release.
Step 3: Publish your package
If everything works, the only thing that's missing is running
npm publish to release the package.
And that's pretty much it. Your package is now live on npm!