How should I use and store this soap so it lasts longer?

To use the bar, wet your hands or body, then rub the soap directly between your palms or against a washcloth, loofah, or sponge to build a lather. Massage the lather over the skin, then rinse thoroughly with water. Avoid rubbing the bar directly on the face and keep it away from the eyes; if soap gets into the eyes, rinse them with clean water.

For storage, place the bar on a soap dish with drainage holes or a ridged tray so water can run off. A bar left sitting in a puddle of water softens and dissolves much faster. Let it air dry between uses, and keep it away from a direct stream of shower water when you are not using it. If you travel with the soap, carry it in a ventilated soap tin or wrap it in a cloth so it does not stick to other items in your bag.

Because this is a solid bar, a 140 g size can last a while if it is allowed to dry out between washes. When the bar gets thin, you can press the remaining piece onto a new bar to use it up rather than throwing it away.