“How you go about doing that, however, is a matter of context”
You’ll need to make the decision on what works best for what you want to accomplish. For OBS, you can do a source (website), a plugin and likely a few more that I am unaware of. For plugins, you can go to here. For pages, you literally make a webpage and handle everything in any one of ten thousand ways.
For Twitch…the API docs are here