How to Cross-Server communication?

I've heard of Cross-Server communication via DataStores since HTTP is too complicated for me to waste time learning but I don't know how to make it work..

Let's suppose I want to send a message to a friend who is in another server. Or even make a modcall request to a mod in other server. How would I send a request to that server to do something via datastore?

Maybe change some values in it using :OnUpdate but idk how.

--This is not a request for a script, it's a request for help to understand Cross-Server communication

There is currently no possible way of cross-server communication that's effective.

You can use DataStores, but that won't be very efficient, and you would need to be careful about the API limit.

Best to do is to use an HTTP server that all servers communicate to for best cross-server communication, as there simply is no other way rather than this or DataStores, a thing I wouldn't recommend.