To fire your weapons, simply tap the equipped projectile button. To the button’s left, you'll see your equipped weapon’s type and grade. 

Your ship is equipped with an aiming assist system. When you align an enemy close enough to the reticle, it will momentarily lock onto the target, improving your accuracy.

HINT: Be careful not to overheat your weapon while shooting. If you continuously shoot, your weapon will enter a cooldown period when you’ll be unable to shoot and be vulnerable. So ensure you’re using your ammunition wisely.