Good for you for being curious enough!
This Chinese character is composed of two characters put together. It literally means JOY, and two put together logically describes 'double joy', or rather DOUBLE HAPPINESS.
The character often appears on (traditional) items associated with marriage and is meant to wish the newly wed couples a long life of happiness.
For me Double Happiness represents being happy and at peace with life in general. It is about the past, the present and the future. So actually, triple happiness..
I have been wearing a gold pendant of this character ever since I left Singapore in 1989 and I had it tattooed on me the day I turned 30.
Wishing you double happiness too :-)