Typically they spawn where ever gigas spawn. Once found one you have to kill some animals preferably a wholly Rhino. once you have the corpse it's a passive tame so makes it better to tame. Slowly walk up behind the Cardo wait till it sniffs the air and run away so it can it can be eaten. When the the hexagon is full above it hop on it as fast as you can and kill everything till it's tamed.