Ah, unfortunately that's the tricky part. Roughly, there are 2 approaches.
Serving from your own computer:
First you need to run a web server on it. If you have Python, running python3 -m http.server 8080 from the output directory is an easy way to do so. On Windows and MacOS I'm sure there are more friendly ways to do so, but I'm not too familiar with those systems.
Then you need to give access to that server. From the computer itself, you can just go to http://localhost:8080`. If you want to give access to the outside world, that usually entails configuring your router to map the port to your computer. That is highly dependent on your setup, so I cannot help much here (that's usual about configuring "NAT" or "port mapping"). Careful, that usually has security implications.
Serving from a hosting service: Here, it completely depends on the hosting service - some will work with FTP, others with SSH, and so on. So, it is hard to give general guidance.
In general, I'm looking for solutions to make it easier (technical, docs, etc.) but there is no silver bullet. The core of the issue is the size of the generated data which makes integrating with simple free solutions (e.g., imgur) not really viable. I might add a specific example later, but that is likely to be based on a paying service.
Ah yes, the github example, fair point. The thing is that Github static pages are limited to 1GB per repository, which will not fit screenshots depending on the generation parameters. Also, Github is not really made for that in the first place, so I prefer not to advise it for this use case too much.