Hey GWolf,
Everybody's got to start somewhere
I remember the first adventure I GMed at your age some... 18 years ago. Dang, it's been that long... We had loads of fun !
So first of all, do you have a scenario ? That's the very basic question. It doesn't need to be anything fancy, and you can have hours of fun with something pretty simple. If you haven't got an already written adventure, I'd recommend designing something pretty simple and low level so that you and your players can familiarise yourselves with the rules and get the idea of how role-playing works. Think something like :
The daughter of the chief of the local village has been abducted by Gobins and they hold her hostage in the nearby caves. The PCs need to go and rescue her.
NPCs don't need to be statted out if you're not going to use them in combat, at least to start with (high level and/or important NPCs may need stats in the future so you know what they can do). As I said above, I suggest starting with something fairly clear-cut and easy to start with, so all you have to worry about is monsters, if you take my goblin idea above.
For monster stats, don't bother about making each monster different if they're going to be numerous. In the example above, maybe you'd have 8 goblins (pick out the stats straight from the Monster Manual), one chieftain (maybe a goblin with a level of fighter added) and a goblin wizard or shaman (a goblin with a level of wizard or cleric added.) You can use PCGen or various online monster generators to generate the more complex opponents.
As for maps and all, here's what you do : you draw your own map of the cave complex (in the example above) by designing a few rooms with maybe possible encounters. For example, one cave could have an underground lake, another one could be the goblin's dormitory, etc.
If you're feeling up to it, you can try to include a number of encounters that do not require the characters to fight. As a GM, you will need to act these out, which maybe a little more complicated but is also a lot of fun (and really what role-playing is all about.) So for example, the goblins could have emprisoned a gnome minor in their caves. He would know where the village chief's daughter is, but he would also like to be freed, and maybe reward the characters with more information. Or maybe, if you're feeling up to it, captivity has driven him mad : he's harmless but will greet the PCs with shouts and hollers, they will need to keep him quite if they don't want to raise the alarm, etc.
One last thing : try to plan ahead so that your first session will have a beginning and an end, especially if you don't know when you'll be playing again. That way, everybody will go home having felt like they accomplished a small quest. They'll want to do it again !!!
In actual game time, you need some paper or plastic board with squares drawn on to simulate the 5ft. steps (you can draw this yourself or buy some) and tokens to represent the characters and their opponents. You can also use cardboard figures or plastic ones of you're feeling like spending money.
Well, that's for basics. I hope I didn't mention too many things you knew already. And remember the most important thing about role-playing : everybody should have fun ! Let us know how it goes !
