What is the role of MBT in modern warfare? Do they fight in mass formations or loss formations? Are they able to move while firing? How does the aiming system work?

Thanks

I am going to say that the main purpose of a battle tank is to break through the enemies front line while at the same time destroying pillboxes, bunkers other tanks etc. so the infantry can move in and they can fire while on the move....

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The war against Russia will be such that it cannot be conducted in a knightly fashion. This struggle is one of ideologies and racial differences and will have to be conducted with unprecedented, unmerciful and unrelenting harshness. -Adolf Hitler

I'm not 100% sure what their role is or how they fight, but I can tell you yes, they can fire while moving (if you're talking about MBT such as the Abrams, Challenger 2, Leopard 2 etc). As for what they use for an aiming system, they have a laser range finder to aim and shoot.
http://www.globalsecurity.org/milita...d/m1-intro.htm
http://www.army-technology.com/projects/leopard/