Gandalf the Grey or white?

i saw the movie and have read the hobit and the lord of the rings trio.
in the fellowship of the rings. he seas to the the balrog in the caves of moria that he was Gondalf the Grey owner of the ring of fire and some other stuff.
but in one of tolkiens other books he talkes about gandalf becoming the owner of the ring of fire when he was gandalf the white.
when did he become the owner of the ring of fire?