There are a couple of possible legends that explain the beginnings of the Claddagh symbol, which you can read about on the Claddagh History and Folklore Page
. But the meaning of the symbol seem to be standard throughout all texts. Basically, it's a collage of elements that represent love, which is why the Claddagh ring is considered the traditional Irish engagement/marriage ring. The same ring can be worn different ways to represent your current relationship status.
The hands represent trust and friendship, while the heart stands for love and the crown signifies loyalty/fidelity. The circular shape of the ring, which can also be drawn into the design, stands for eternity. Sometimes the Claddagh is also accompanied by a cross, which represents faith. So, the Claddagh has many significant meanings all wrapped up into one pretty design.