First, you need to connect to the event, to do this you must obtain the "Event Code" from the host, enter it in the text box on the homepage, and click "GO".
Once you're connected to the event you will be presented with two options, "Record Video" and "Upload Video".
"Record Video" allows you to create a video in the browser. Click the option and a camera view will appear. To film your message, either click "Record" located third along the bottom bar or "Start Recording" just above the bottom bar. To adjust the zoom of the video, slide the bar located at the top of the page.
"Upload Video" allows you to choose a pre-recorded video to send. Click the option and it will ask to access the relevant apps on your device, browse through them and select the correct file.
When you are happy with your video, click the "Send Video Message!" in the green box at the bottom of the screen.