You can add items to your meeting's Playlist to share with your meeting participants.
From the web, the globe icon at the top, select YouTube, Flickr or Photobucket to search a video or picture. You can then type in your search item in the bar at the right.
Once you select a video or picture by clicking on it, the item will load to the front end (extreme right) of your Playlist.
You can always drag Playlist items into the order you prefer, and you can select an item at any point on the Playlist to share it on the Stage.
If you want to upload a file from your computer simply select Content (the icon that looks like a sheet of paper with a folder corner). Click on the Upload button to search for files on your computer. Once you've chosen a file and opened it, the file will upload to your content.
Once you select a file by clicking on it, the file is placed at the front end of your Playlist.
To upload a Whiteboard onto your Playlist, click on the tools icon at the top and select Whiteboard. If you X your Whiteboard offstage, it will still be available to reload to the Stage from the Playlist, so that you can see your last markups. However, if you delete a Whiteboard from the Playlist, you have permanently deleted that Whiteboard.
Uploaded content is different. Any uploaded content you delete from the Playlist is still available in your Content section, unless you also delete it there.