Once you are logged into your Website Builder you will see a content icon on the top left side of the menu. There you will find the option to add a Video to your website.
You can then copy/paste your YouTube video address and the video will appear on your website.
YouTube is used as you can upload your videos and embed them on your page (or pages).
You won't have to worry about the format as YouTube will automatically convert it.
By default, your YouTube video will be full-width, you may want to add a column content block and drag it to one of the columns.
One more option is to use any of the images on your page and make it a link, using your YouTube video as URL: it'll automatically create nice looking "play" icon on it, which when clicked, will open the video on a lightbox.
