It's basically about this girl and her horse, who are the best of friends. Her horse is named Wildfire. One year, during a blizzard, he breaks out of his stall, and she goes to find him. They both...
If you mean the French words... "Sont les mots qui vont tres bien ensemble" means "These are words that go very well together"; a French equivalent of the English lyrics.
The term "fly" according to the Urban Dictionary suggests it's a slang term for something that is "cool" and "in style." The lyric "fly like a G6" probably refers to someone/something being as cool...