First Time DM - How Do I Prepare?

Quote from Beef_N_Cheese >>

yeah, im extreamly new 2 dnd and everyone else in my party knows how to play but i got roped into being a dm. everyone else has years of experiance

 If you don't mind me saying that's incredibly unfair of your friends to do that, being a DM is very much about knowing the rules and how to implement them so a bunch of people who know how to play expecting someone very new to do the most complicated job at the table when almost any of them would be better suited is them taking the piss.

Having said that if you can't get anyone else to do the job and you are lumbered with it then time to learn how to play. Read the basic rules, they're free on this site and a lot less intimidating than reading a 300 page book. Next up go to YouTube and look up a video by a guy named Matt Colville (Link to episode 1 is here https://www.youtube.com/watch?v=e-YZvLUXcR8) He did a fantastic series on how to DM that started 10 years ago, you might find DM how to videos you prefer (I personally like a channel called Mystic Arts) but Colville is both informative and reassuring so a good place to start.