Happiness? Not that simple. Where does happiness come from? Most rationals would answers evolution. If that's the case, then it should have a function. Figure that one out and you will also learn how to become happy.
"Happiness" is a vague emotion, like love, not an objective, short-term, measurable one, like calm, contentment, or excitation. However, all states of happiness usually share in common a factor of endorphin release.
Endorphins are basically one of two basic mechanisms for "fitting" data in the brain-as-neural-net, with the other being pain: pain is the reinforcement mechanism that trains your neurons to not do that again, while endorphins tell your brain to do please do that again. People are "happy" (have endorphins) when they're doing things that their body encourages them to do. To be happy is simply to be one with your body's material desires (though note that your brain is part of your body, and it has material desires of its own, for things like friendship.)
