Happiness is a bit of a tricky concept, and it's not very easy to define, as it's very subjective. On one level, I think we tend to think about it as that "up" emotional state - but I don't think that's a realistic goal, because there are highs and lows in life. So we need to take a broader view.

Something that i think is more useful - easier to understand, and easier to apply - are the concepts of positive psychology. Martin Seligman (who wrote Flourish) has a 5-point model of emotional wellbeing: PERMA

Positive emotion - spending time doing what makes us feel good,eg spending time with friends/family, getting into nature, whatever.
Engagement - this is about doing things that you're really engaged with, that put you into a state of flow
Relationships - this is about being connected to other people
Meaning - this is your sense of being part of something bigger than you, having a sense of purpose.
Achievement - these are your accomplishments.

These five areas are strongly correlated with high levels of personal wellbeing. I highly recommend you have a look at some of Seligman's work, there are youtube videos and he has a website where you can do some questionnaires, etc. There have also been a few telly programs on the ABC over the last couple of years, like Being Happy and Making Couples Happy.

I'm not sure that it's something you can decide at short notice, kwim? But if you start asking questions, thinking and getting some evidence-based tools (eg, like the positive psychology stuff) then you'll be able to grow your understanding of what it means to you, and more importantly, how to live your life so that you're accessing as much of that as you can.