Step1: Find and talk to Ranald (NPC), the Combat Arts teacher at the school
To become a great warrior, you must first learn the basic skills of combat. Practice your skills on the training dummy under the tutelage of Ranald!

Learn basic combat skills!
If you hit the training dummy more than once, you will attain Combat Mastery Skill. Open the Skills window (press 'S') and click on the 'Learn' button in order to acquire the skill. Once you learn this basic combat skill, if you talk to Ranald again, and he will teach you the 'Defense' skill. Continue to practice these skills so you don't forget them when you engage in real combat!