When you create a post or message, you'll have a text edit toolbar at the top of the text box. In that section, you should see a button labeled "Add a video".
Here's how to add a video:
1. Click on the "Add a video" button.
2. Select the tab to choose the location of your video. Paste the image URL into the text field.
3. When you're finished, click "Insert".
Note: Videos cannot be added when using a mobile device.