Your objective in Super Battle City is to search and blast all enemy tanks with your trusty turret gun. Defend your base from enemy fire, and while you'll just respawn if you're destroyed as long as you have lives left, if your base is taken out, it's game over.
While a lot of things in your environment are not only destructible but filled with coins to spend on upgrades, you might not want to just start blasting away willy-nilly, since a lot of that terrain can be all that stands between you and total decimation by greater enemy numbers. Power-ups can be found to temporarily boost or shield you, and if you capture a turret by sticking close to it long enough.