I don't FUСКING get the tank campaign

I'm a new player, and playing tank only brings me frustration. Why when I shoot at green spots it's "hit" mfs when they shoot me anywhere I get one shotted? Any tips because I'm boutta tweak out

I'm a new player, and playing tank only brings me frustration. Why when I shoot at green spots it's "hit" mfs when they shoot me anywhere I get one shotted? Any tips because I'm boutta tweak out