what the title says, how does one post videos on the forums?
You just need to copy the URL and paste it on it’s own line. Like so.
Like @Shunty said.
If you have a video on your PC that you want to put on the forums, you need to upload it to YouTube/3rd party video sites, then copy and paste the link in a post.
The reason is because Discourse (the forum template/host) does not have an embedded video player.