I am kind of confused on how to use sync pokemon? For it to work do you just need a sync pokemon and it is a 50/50 chancee to find same nature any pokemon. And also can it be fainted in 1st slot?

@Cathater Yes, you need a Pokémon with the "synchronize" ability. Pokémon such as Abra, Natu, Ralts have it. When hunting, put the sync (with the desired nature) in slot 1 of your party. One thing people like to do is use a high level / LV100 Pokémon with the move False Swipe, to bring the HP down to a minimal for catching (this Pokémon put in slot 2). The sync will still be in use as a fainted Pokémon in slot 1, so you don't have to worry about that. However, as you've said, its a 50/50 chance of synchronizing the nature