It is a starter kit, so you don't need to have your own character ready to play the game. Though, it can certainly be enjoyed by people who already love the game since it's a tie-in that doesn't lean too heavily on your love of the show.
The kit comes with dice, a rulebook, an adventure book for the dungeon master's eyes (featuring a drawing of Will the Wise on the inside cover and a cover that matches the design on the front of Mike's book on the show), character sheets, and two Demogorgon figurines (one of which is unpainted, ready to be customized). The game is nice for beginners, as it's simple and straightforward and not too bogged down in the expansive universe you see in many 5th edition starter sets. The character sheets allow you to play as Mike’s paladin (human), Will’s cleric (wood elf), Eleven's wizard (half-elf), Dustin's bard (hill dwarf), or Lucas' ranger (half-orc). Sorry, Mad Max fans. No Zoomer.
The brief adventure available in the box is "Hunt for the Thessalhydra," as played by the kids in Season 1. The game is now available from Hasbro Pulse, local game shops, or online retailers like Amazon. (It also appears you can buy a digital version of the adventure at a discount with none of the other starter kit materials.)