It's a mystery.

I want to make a mod for a car from the game, but whenever I open a blender file from the car, a cube pops up. (I know, I'm new.)

 

Delete the cube, your car is likely hiding inside it

 

delete the cube, use the import function

 

I don't know which type of item it is. Is it a .obj file? Is it a .dae file? (It's the Autobello, that's all I'll say.)

 

dae

 

If you want to import something else than a .blend file, then you need to do it through File -> Import (then select the .dae, .obj or whatever it is). Dragging & dropping works only for .blend files

 

How do I drag and drop? I tried it a few times but nothing seems to work.