The ones I've fitted have had the holes pre drilled in the door so you know that's what you should do.  Others have used very strong contact type adhesive pads to secure the bracket to the fridge door.

Seems strange they don't indicate what is required?

I assume the type you have are the two piece, where one (the slider) is screwed to the cupboard door and the other (the bracket) is fixed to the fridge door?

The other type I have come across actually have the cupboard door rigid fixed to the fridge door with no hinges on the cupboard door at all.  The fridge door has special 'reflex' type hinges to throw the door away from the carcass when opening the fridge.