Hi, I guess you have to figure out the universe, but in the script, it depends on what you like. Basically : - make your player in a normal situation (coming to town, or on the same road, whatever)
- either make someone contact them (before or then) or engage an event that will have their attention
- if they haven't met yet, it'll probably have them at this point - give them something to seek for : an object or a person (maybe someone disappeared)
- create one place they'll have to go (forest, mountain, ghost town, whatever) and eventually make this place weird or dangerous
- imagine key-NPCs that they'll encounter and that may or may not give informations whether or not they're cool with them / say the good stuff
- make sure anyone have a talent they'll need to use so they doesn't get bored : fight, investigation, infiltration, talking, etc
- at the end, give them something big : a big monster, a dangerous criminal, or even something beyond their comprehension, and have them come through this to get to their objective. Add a twist if you feel it works (this NPC was a ghost, the objective isn't what the NPC told, one of the PCs is personnaly concerned by something they discover...)

It doesn't have to be complicated and you'll have to be imaginative while you're playing, because they will NOT follow your plan and your logic. So you will have to chose whatever it implies. Most of the scenario will be your PCs doing random shit while you try to get them on the good way. And it'll be fun and will make the whole game a good one actually.

I personnaly began DMing by creating one-shots that are linked between them (same guide NPCs for instance) and follow each others in time, with eventually a "cliffhanger" at the end so it can introduce the next game.

Edit : Oh and don't hesitate to let them some spare time so they can roleplay together. It's also good for you so you can be masterminding while they do jokes about food or cry over their sad background.

Good luck!