A Checkout Message is a way for you to send in a message to any currently live Linus Tech Tips or WAN show stream. When checking out on LTTStore you will find a form on the cart page that takes information about how you want your message to display and what you want the contents of the message to be.
When you submit a message the producer for the livestream has a dashboard where they can reply to your message directly and you will see a response after yours on screen. Alternatively, the producer may curate your message, which means they will read your message aloud to the host for the host to answer.