CreatePersistentEntity("ScoolBus")
There's more to that function than just the string. I recommend using the number ID for any prop, but we'll stick to "ScoolBus" for this example:
CreatePersistentEntity("ScoolBus", x, y, z, rotationInDegrees, areacode)
For areacode you should just use AreaGetVisible() and it'll use whatever area is currently loaded