Does anyone know where I could find a tutorial for creating a scene where a character will automatically talk to me as soon as I enter a room, and then proceed to attack me.

Probably better to use a force greet package and set your topic to your dialog info. Them set him hostile by setting a faction or actor property. Have you gone through the basics of packages and dialog?

I know how to do dialogues, but how do you do the force greet package?

Create a new package and set it to ForceGreet in the Package Template. In your Public Package Data, select your topic dialog topic and trigger radius and target. Set any schedule you may need and conditions and add it in your actors stack or alias in your quest if you made one.