Welcome

First of all you need a webserver/webhosting to actually store it on the web, unless you do it localy (http://localhost/) but no one will be able to access it only that pc!
But get ya self a cheap web hosting plan, like Go Daddy or 1and1 and use it has a ftp server.
Then all you have to do is connect to that server with an ftp client such as Filezilla. then navigate to the directory you want the "json" file to be in, and just drag ya file into that directory. and your away, and just use your domain to visit the file like www.example.com/yourfile.json

Ps:
i dont really do web develupment anymore, but im pretty sure thats how it works.!

You can host local server on your pc but you'll need a ddns, port forwarding and keep your pc up and the most important online 24/7

Well that's the way my main site works 😂. I am just running a web host on my computer... it got not so awful uptime