There are several different "celtic paths" depending on where you are from such as Irish or Scottish etc. and they vary a bit. Druidry would be the best thing to check out for information as was stated above. It is a mostly nature based path involving many different deities.
As I see it, being a Celtic pagan is not the same as being a Druid. I am learning the Irish Celtic traditions including practicing magic. Incorporated into that was learning about the Druids and the Four Powers of the Magus. But I am learning how to practice magic in the Irish Celtic manner. That does not include becoming a Druid or obtaining the knowledge Druids must have.
The way I see it, Celtic Druids are primarily teachers and not practitioner. Celtic Pagans are primarily practitioners not teachers.