Serotonin makes me happy
At least, that is my understanding of it, a chemical is unleashed in my brain and hits all of my happy spots, sprouting a sense of euphoria.. That understanding of neurobiology may have since changed though, so I could be completely incorrect in my assessment of happiness. On a more general, and serious perspective of the question, a lot of things can make me feel happy, it could be something as simple as seeing the moon sitting in the sky, or the way a tree sways in the wind. It might be sitting back at my computer, after cleaning the house, there is a large variety of things that could make me feel happy. Usually, I can produce a sensation of happiness, if I really want to, it is a matter of finding significance in anything, really. A trick of the mind, if you will
Emotions are pretty interesting, and over the years, I have become pretty good at manipulating mine, I'm trying to find an analogy of what it is like. Fishing comes close, although, I know little about fishing, but from what I have seen, it seems similar. You know the good spots, you get a feel of your line, you know which bait to use to catch the right fish. When you feel the tug, you know how much of a pull you need to take, how to reel in the fish, and not lose it in the process, and you also know when it is just a boot or weed. It is a cheesy analogy, but I think it fits pretty well.
Of course, there are bad fishing days as well, and no matter how many tricks you have, you aren't going to catch any.