Not as essential as the others books
I'm a new DM and new to tRPGing also. I read this one first and it gave me a good overview of the game. It gives you lots of content in terms of magic items (about 1/4 of the book), different modes of play, exploring the planes (an annoyingly large part of the book, and right at the start! I recommend leaving the planes until last or until you want to read about them) and combat rules (flanking, for some reason, is an optional rule, only contained in this book and not the PHB)
We put labels in it and use it to randomise encounters for our rotating-DM game, but it's not always easy if your creative juices aren't running and you haven't had time to plan either. If you want to get into the game, I recommend you just get the Players Handbook and a published adventure (like the starter set, or one of the newer ones) before creating your own campaigns.