To upload a video from your computer:
First, make sure that your video follows these specifications. (link)
Click the Browse... button in the object browser window.
Select the file you want to upload from your computer then click Upload.
When the video is finished loading, the filename will appear in the attachments list.
Click the icon next to the filename to select the video.
Then click Update.
When the page is updated, the video will be displayed.