It's where you can pay a celebrity of your choice to record a personalized video message, aka shoutouts. They have actors, athletes, models, musicians, "influencers", YouTubers, wrestlers, drag queens etc. You could, for example, arrange for Flavor Flav to congratulate your son on passing his exams or wish your uncle good luck with his surgery or whatever.
I'm tempted to use it myself, actually. My Mum has always had a thing for Nigel Havers (as do most women of a certain age, seemingly), and he's available for the alarmingly low price of $25 per message. I could ask him to record a pleasant little Happy Birthday message for her next February, I reckon she'd be genuinely thrilled.
Sylvester McCoy has been known to record his shoutouts in character as the Seventh Doctor ("Greetings from Gallifrey, earthling!"), one for @The Weeping Angel