How to pass userscript data from the form to itself?

Question

userscript

There is a site where the form is filled out.
How to make a userscript that, when you click "ok" on this form, send the data from the form to me in a file, in a database, or somewhere else similar?
Questions, actually, such:
1. How to intercept press OK.
2. How to send data. Is it possible to write to a file? Or is it necessary to raise a web server that will accept json? Or a database, I don't know.