It has a mark for 50yds, 100yds 150, 200, 250, and 300yds. at about max power, ie 2 pellets, 3 pellets or shotgun setting, those marks will be where your bullet hits.
the 100yd mark will be accurate at low/high/any power, all of the other marks will change with a power change.
If you shoot a deer at less than 100yds, that center cross hair should hit the deer at any power, if over 100yds, you'd want that 7x or 9x, which btw, those 2/3 pellets shotgun setting isn't max power, so it may actually be 8x instead of 9x. At a long shot on a deer over 100yds you'd want max power, for stalking / close shots, low power and that center cross-hair will be fine.
It sounds more complicated than it is.
It's a great scope, I have the 3-9x