You do not upload videos to this forum... you upload them to YouTube or Vimeo... then you embed a link to that video. In the posting navigation bar (above where you type), there is an icon of an ellipse and a dropdown arrow, to the immediate right of the emoji. That is the Insert Menu... click on that dropdown menu, and choose "Media"... In the popup box that comes up, paste the URL of your uploaded video... click "Continue".