At the moment, we only support adding YouTube videos on your Posts. It is not possible to upload videos to Similar Worlds.
Copy the link of the YouTube video you want to include on your post:
Then, on Similar Worlds, press the following button:
In the window that opens, press "Video", and then copy the link into the text box:
Press "Insert YouTube Video" and the code should appear in your new Post text.
When you submit your new Post, the video should appear for everyone.