Get the shower jelly wet, lather right on your skin or using a loofah or shower pouf. Then rinse off.
You can choose to refrigerate them or freeze them too, which makes for a really cool fire-and-ice kind of shower experience. And gives them a little more of a solid texture. They can be a bit slippery at room temperature so if you find yourself droppin' that slippery soap too much, toss them into the fridge or freezer next time.
It's also best to place in a container and drain out any excess water after using so they don't get gloopy. Or get your pouf or loofah wet, then rub it into the container with your shower jellies and lather it up that way without getting the whole bar wet.