An Apple Slicer is a device designed to both core and slices apples. There are simple hand ones that work through brute force, and machines that work through hand cranking.
The simple ones look like a wheel with spokes. They are a large round metal ring, divided into eight sections by metal blades, converging on a smaller, centre ring. The smaller centre ring is meant to tackle the core. The eight sections are meant to produce eight wedges of apple. On each side of the ring are handles used to press down with.
You can peel the apple before starting, or not. If you don't peel it first, don't forget to wash it first, though. You set the apple upright on a cutting board, line the smaller, centre ring up with the centre of the apple, and press down hard.
You can use also use these simple ones on potatoes to make potato wedges.
The machine ones have a suction base or a clamp to grip work surface with. The clamp-on ones often require some sort of "overhang" on your work surfaces. At one end of the machine, you have a fork that you skewer the apples on, putting the tines through the centre of the apple. Then you swing the attached peeling blade into place, just touching the skin of the apple. You turn the hand crank at the end other, which turns the apple against the blade, peeling, coring and slicing it all at once. These machines are very efficient at processing large quantities of apples. Some models allow you to take the slicer knife off so you can just peel and core, then slice on your own as desired. It will make very thin slices; you can also attach a potato to it for scalloped or dauphin potato dishes. The uniform slices are also ideal those who dry apple slices in a dehydrator.
The machine types work best with apples that are perfectly shaped.
Afterwards,with either type of device you may need to trim to slice off the slices any bits of the core that survived or any of the tougher husk-like cavities that encased the seeds.