Shock Armies were a product of the Soviet Pre War doctrine which called for the application of "shock power" and the combination of multitude of arms and services to inflict a decisive defeat on the enemy and drive deep into their lines. To this end Shock Armies received significantly more artillery and armoured forces to aid in breaking through tough enemy defenses. They were used to attack and smash through enemy strong points or areas where it was perceived the enemy could be weak and easily broken. In theory anyways, in reality they were deployed where they were needed regardless of the situation and depending on the strategic situation at the time. Here is some of the operations the shock armies were used in. The 2nd Shock Army was used in the Moscow counter offensive and succeeded in breaking through the German lines before being cut off and surrounded. The 1st Shock Army was one of the reserve armies Stavka used to reinforce Moscow. The 5th and 3rd Shock armies played huge roles in fighting in Berlin with the 5th taking many of the suburbs and the 3rd being the one to take the Reichstag.

This document gives a good idea of Soviet Doctrine and the use of shock armies.

http://www.fas.org/irp/doddir/army/fm100-2-1.pdf

Some books on the subject:

When Titan Clashed by David Glantz

The Fall of Berlin Antony Beever

Thanks! Where these armies where most of the Soviet casualties occurred?