Most, probably nearly all fans have arrows on them, like this:
If you point those arrows towards the case, and mount the fan using the rubber fasteners or screws, you'll have it right. If the arrow that points (not sideways, that's the wrong arrows) from one side of the fan to the other side of the fan is pointing into the case, it will be wrong. It should point towards the outside.
I don't know what else you'd need to see a picture of. If you look on the frame of the fan, there will be arrows on one of the four sides.