Your characters will have roles, known as Paradigms, assigned to them after a bit of progression in the story. Characters are limited to three Paradigms, orientated towards their proficiencies in battle and they are as follows:
Lightning - Commando, Ravager, Medic (unlocked later)
Sazh - Commando (is unlocked later), Ravager, Synergist (unlocked later)
Vanille - Ravager, Saboteur (unlocked later), Medic
Snow - Commando, Ravager, Sentinel
Hope - Ravager, Synergist, Medic
Fang - Commando, Sentinel, Saboteur
Once you've unlocked Paradigms, the battle screen will be updated with a few new goodies. In the lower left corner of the screen you have two additions:
a) Paradigm can be accessed by pressing L1/LB. What does it do? It allows you to change characters' roles in battle on the fly by choosing one of the predetermined setups you created (you can have a maximum of six setups).
b) Techniques command has been added. Techniques are special commands which use up Technical Points. Technical Points are not infinite, so use them sparingly.
In the lower right corner of the screen, the following info has been added:
a) Between the character's name and the numerical HP display, you'll see a shortened name for the character's role - COM for Commando, RAV for Ravager and so forth.
b) The Technical Points gauge has been added below the leader's HP gauge. The Technical Points gauge decreases as you use up TP, and can hold a maximum of 5 Technical Points. The Technical Points gauge slowly recovers during battles, and can be fully recovered by using either an Elixir or Ether Smoke.