Running a game of Dungeons & Dragons can be incredibly intimidating, but it doesn't have to be. There are some simple things to help you as the DM and your friends' first game go as smoothly as can be expected for a first-timer!
These are my personal recommendations - there's a lot of different ways to run games, but this is how I now run my games and I think it streamlines a lot of things.
Use D&D Beyond
D&D Beyond is the "official digital toolset for Dungeons and Dragons" and I LOVE playing and running my games with it. If this is yours and your players first time playing (which I find to be mostly the case - 5th Edition D&D is adding new players every single day!) D&D Beyond is a great, but mainly cheap way to run your games. Just by signing up, you have access to 5th Edition's Basic Rules, which is enough to run your first game. There's also a built-in Character Builder, which makes creating your first character a breeze.
Don't want your players to be on their devices when you run your game? No sweat - still have them create their characters on D&D Beyond; it can export their character's into a PDF they can print and bring with them!
Prefer the feel of total pen & paper? Here's some links to the official free content you can download and print at home!
Confused on how to create your first character? I'm going to be posting about this subject soon, but in the mean time check out this great article from Nerdolopedia.
Buy your first dice set
D&D uses different sized dice for different things - the most famous being the most commonly used: a twenty sided die, aka the d20. The standard set uses seven different dice: the d4, d6, d8, d10, and d20. The number in the name of the dice represents how many sides the die has.
It's really easy to a set of RPG dice on Amazon, but I would encourage you to go your local game store to pick up a set! Not only does this let support a local business, but you can make a connection to the owner and employees there! If its a game store with their salt, they have D&D groups that play there regularly. Your game store is your access to your local D&D community!
For stores that have registered with Wizards of the Coast, use this link find one close to you.
Of course, not everyone has easy access to a game store. In that case, why not check out some small businesses on places like Etsy or Ebay? Really cool dice are just a Google search away.
Run the starter adventure, written by Wizards of the Coast
I've run this module multiple times and I think its the perfect adventure to get started! Using a pre-made adventure is a great way of taking some of the stress and pressure off of you, the DM, so that you aren't having to come up with something yourself.
The adventure I recommend is called "Lost Mines of Phandelver" and its available on D&D Beyond, just like any and all official Wizards of the Cost content. It'll only cost you $15 and it will give you the full adventure, which will take your characters from Level 1 to Level 5. This should easily last your group several months, even if you play once a week. In that time, you'll be able to familiar enough with the game.
Buy the main set of rule-books in this order: Player's Handbook, Dungeon Master's Guide, and the Monster Manual. All of these books are also available on D&D Beyond.
You might be visual learner like me, so here's a great video from Geek and Sundry's show Starter Kit, where a DM plays with some new players. It doesn't show you everything, but it does show you a good bit.
I hope this helps! Know that I believe in you - I was where you are a year ago and while I still get nervous before every session, my confidence grows with every session I run.
Get out there and game!