Kitties take care of all their needs automatically as long as there are ways to do so. They will take care of “Play” in many ways (chasing your cursor, playing with toys, playing tag, etc), they’ll take care of “Clean” by licking themselves, and they’ll take a catnap to fill their “Sleep” bar.
Happy is the only exception, it increases slowly over time as long as their other needs are not empty, but also eating good food, playing with yarn, and petting them will increase their happiness.