You can only have two turrets out at the same time on lvl 3
Turrets deal half damage to towers.
Try to stay behind the turrets.
Turrets are close range so you need to attack or attract the ranged.
Place two turrets at the same spot.
If an enemy hero comes near you and your turrets use upgrade,exaust and skills.
Placeing turrets beside a tower becomes great defend.
Put your points in turrets and upgrade when you can.

Bye much ability power and some mana.