The combat system in Final fantasy XIII got some differencies with the previous chapters of the saga. So you can still find the command menu which will offers you five choices with a cost for each. You will also find the Action Time Bar which determinate the remain time of your turn considering the cost of the competences you have choose in the command menu.
A chain and bonus indications will also appears on the screen, chain is the amount of hit you have done and bonus is supposed to be a kind of Limite Break you found in FInal Fantasy VII. In this chapter you will also see the life and the name of your opponents and will have no transition between the meeting with monsters on the map and the battle screen.

(Source : Famitsu)