Abbby I don’t know which video you’re referring to but you should be able to upload videos by starting a new post (New Discussion or Reply to an existing discussion) and then clicking on the button at the bottom of the text entry box that has a video icon “My Media”.
Click the Upload button at top-right and select the file from your device. When it finishes uploading, select it to add it to your post. I think that there’s a max filesize limit of about 100 MB.
If you have a link to a video on another site that is publicly accessible, just post the url from the address bar.
