You just need to choose the Company Commander Tree you like, If we Examine All the Faction. The Left is the one that focuses on Defense and Artillery, the Middle is Focuses on Surprise Attack, Intelligence and Fast Attack, the Last one (the Right one) is Focuses on Building Ultra Strength but Slow.
You can choose the Company Commander in the flashing green button above the Mini-Map. After that you can gain Experience by Building Army, Capturing points or Attacking the Enemy. You will notice that the number on the Green Button is Growing! And then you can choose unique Powers from it!
Attacking enemy with powers is critical to your success in Fighting your Opponents, Usually when activate or use the power you need resources so keep an eye on both of em!