To add video to a creative you're building with Google Web Designer, drag either the Video component or the YouTube component to the stage.
If your video is hosted on YouTube, use the YouTube component.
If you want to use a MP4, OGG, OGV, or WEBM video file, use the Video component. If your file is a different format, you can either use video editing software to export it into one of these formats, or upload it to YouTube and use the YouTube component instead.