This is my recommended DM starter kit! For real, taking up the mantle of Dungeon Master can be intimidating. Having the right tools from Wizards of the Coast means you can keep the emphasis on immersive story telling through-out role play and combat.
While the Player's handbook covers all the rules you'll need to know, the Dungeon Master's Guide expands your arsenal of world-building tips, alternative rules to suit your play-style, and a cornucopia of magical items to bestow on your adventurers. The Monster Manual provides a non stop shop of creatures to help and hinder the party and keep them guessing about both the horrors and wonders they'll face.
Nothing makes you feel more like a DM than your very own screen! Confidence only grows when you can spread out your notes, miniatures, and more under cover of darkness! You'll have combat actions, DC ratings, and condition rules all at your finger tips. Character Condition Tokens give you the tools to run monsters with more complicated abilities, track any conditions they force on the party and keep your friends on their toes as you increase the challenges they face.
Adventure Grids allow you to quickly sketch battlemaps with wet erase markers and ensure faire and equitable combat for both Dungeon Master and Player Characters.
Lastly, a tool that will follow you to any role playing system is Paizo's Starfinder Combat Pad. Magnets allow you to track initiative order for heroes and villains and rounds - as well as make notes about hit point totals in wet erase marker. This is truly one of the best tools on the market to improve your game.
With these basic tools, even brave new DM's will be ready to roll!