How to set up server on your computer and broadcast it all over the Internet?

Hello, I've been recently struggling with establishing a connection between my computer and anyone outside of my local network. As a starting point I've chosen to host a simple http server, and be able to access it from the Internet. (i know there are many easy to run services, but that's not what I want)

I tried to connect to my ip address, but with no result. If I can browse websites or play online games, it means the servers are able to connect to me. Maybe it's only possible after I make a request to them?

I also did some investigation with "traceroute" command and i found that all my requests pass through some server from my internet provider. Also, my computer sees an assigned ip address that is different from the one I see, when i type "my ip address" in google. It means that I am connected to some subnetwork of my internet provider and all requests pass through them. But how the external source is able to connect to my computer, how the subnet knows where to forward their requests?

I need any theoretical knowledge about concepts I described (names), and tools to inspect connections between computers. I know basic stuff about http get requests, I want to know how external sources are able to connect to my computer, even though I am connected to some subnet.

Do you know anything that would help me in some way, or help me achieve my final goal, that is hosting a server to the Internet from my imac? Is it possible?