Here's a basics/fundamentals video on how to cut up an apple. This is how my chef in school taught me and I find that this is the fastest way for me. In the industry, most places that use a ton of fresh apples have a peeler, corer, slicer all-in-one gadget that you can find at places like Bed, Bath, and Beyond. The rest of the industry tends to just buy instant quick frozen apple slices. I hope this is helpful!