How to create a package.json with a list of used plugins in an already started project?

Question

gulp.js

Slightly incomprehensible moment.
When deploying the project, I manually created package.json and then installed each plugin separately.
As a result, it turned out that package.json was left empty.
Please tell me, is there a command that allows you to create a package.json with a list of plugins used in an already started project?
And how is it correct to create it at the beginning of the project?
Thank you!