What screws to use to hang bathroom mirror cabinet?
Really, any wood-thread screw that penetrates your framing (studs) at least an inch will do fine. Depending on the back panel construction you may want to use countersunk flat-head screws or pan-head screws. (You wouldn't countersink screws in a very thin back panel.)
If you have steel studs you'll need a sheet metal screw, and I'd use a few more (six rather than four, say).
Drill through the back rails if your cabinet has them, otherwise drill fairly near the top and bottom panels. Putting screws toward the vertical center can lead to sagging when the back panel bows. Don't use the pre-drilled holes unless they align over studs or you use hollow-wall anchors designed for the type of load you're installing.
Try to be aware of what plumbing and electrical hardware may be in your walls and avoid damaging it.
Use a bubble level or a tape measure (from the floor, wall, or ceiling) to set it level.