The chapter: “Thirty spokes share one hub. It is the empty centre that makes the wheel useful. Clay is shaped into a vessel; it is the hollow that makes the vessel useful. Doors and windows are cut into a room; it is the emptiness that makes the room useful. Therefore: what is, gives form; what is not, gives function.” (有之以为利，无之以为用.)
The teaching
Everything we value in a thing comes from what it does not contain: the wheel’s usefulness is the hole; the cup’s function is the space; the house is the volume, not the walls. The chapter’s claim is general: the tangible gives the form; the emptiness gives the function. And what is true of objects is true of lives — which is where the teaching bites.
Applied to a schedule
A calendar with every hour filled is a wall with no room. The useful day has empty centres — the gap between meetings, the unscheduled evening, the hour that belongs to no one. Lao Tzu would say: the filled hours give form to the day; the empty hours give it function. Schedule the gaps deliberately.
Applied to a home
A room stuffed with furniture has form and no function — no space to move, gather or breathe. The feng shui principle is the same one: keep the centre clear, because the emptiness is what the room is for. The feng shui tradition and the Tao Te Ching agree on this chapter.
Applied to a mind
The most personal application: a mind that is always full — opinions, plans, judgements, self-talk — has no capacity for the new. The Taoist practice is to keep an empty centre in the mind: the stillness that receives, the pause before the answer, the not-knowing that allows genuine learning. The first chapter said the Tao is not the words about it; this chapter says the capacity for the Tao is the emptiness inside the words.
The one-line version
Fill less, so the thing can function. The wheel, the pot, the room, the day, the mind — each works by its hollow. Leave useful emptiness in yours.
Dig deeper: the Taoism page and Chan meditation — free, deterministic and in plain English.