There's a fine line between under-kneading and over-kneading biscuit dough. Kneading dough encourages the development of gluten. A tiny bit of gluten development is important to the structure of biscuits and will help them rise and not collapse on themselves after baking. But too much gluten development will make the biscuits tough.  Once the ingredients have been mixed (step #6), use your hands to gently knead the dough, just a few times, until it is mostly uniform and holds together. The dough should be loose structured, but still hold together as a cohesive dough. If you're uncertain, err on the side of under-kneading. Under-kneaded dough will make tender biscits that are still quite delicious, they just won't be as tall as the ones pictured here. Over-kneaded biscutis will be quite tough.