Legal custody - what does it mean

No separation agreement signed yet. I have my daughter all but one day/night a week when she goes to her fathers (but not always every week). She is 12.

He is now argueing over Legal custody (he agrees for me to have physical custody). I just figured that since I have her the majority and take care of her I should have legal. If I give him joint legal custody what exactly does that mean for me?

Question2 - If i have legal custody can he take her out of state without my knowledge?

Unless he is unfit in some way the court would probably award joint legal custody. The parent taking a trip with the child usually gives the other parent some notice of the trip.