This is one of those things where if you have to ask how to do it, from a practical perspective, you probably can't.
You'd need to run your own RTMP server, your own webserver, stream from OBS to that, and then embed a player in a web page, and port forward on your router to the machine running the webserver so that the public internet can access it.
If you aren't already familiar with those things, doing them is non-trivial and potentially presents a security risk to your local network.
However it is technically possible. However I would not recommend it for a new OBS user, this is not really a basic function.
Most people who stream enjoy using services such as Twitch.tv or Ustream to deliver video to viewers, and that works well enough. But sometimes you want some more control over your stream, or you want other people to be able to stream to you, or...
obsproject.com