As the title says, I'm a bit confused about how HDA's work in Unreal. Ive just imported a fairly simple, but by no means low-poly scene, via HDA into Unreal Engine and have not had to unwrap it, polyreduce it, or anything else. I haven't tried to apply textures yet, but is seems mind boggling that this is possible. The model does look a little simplified - the geometry is way less complex, but nevertheless im just really confused as to how it works.

Could 1) someone just tell me what actually happens when you make an HDA and 2) also maybe offer some advice onto how I should texture this. The scene is divided into the different parts (i've grouped the different regions of the scene to in order to texture (it's split into Mat/shader groups) - but this information doesn't show up in UE4, which would have been handy as I could have just used UE4 shaders. Do I have to bring in my own textures/shaders from elsewhere?

Thanks in advance