Only the gel stored inside the leaves is harvested for edible or topical use. Typically, you’ll find large aloe leaves available in grocery stores near the exotic fruit section, but to harvest from a plant, clip off a leaf near the base.
Take your aloe leaf and trim off the serrated edges with a sharp knife. Fillet off the skin like you would a fish, removing all the skin and the yellowish layer, leaving behind the clear gel at the centre. You can use a sharp knife or vegetable peeler. Alternatively, the leaf can be sliced lengthwise and the gel scraped out with a small spoon. The skins can be composted.