Contribution can be earned directly from completing quests, or by gaining amounts of EXP towards unlocking additional points through quest completion.
Starting out, do as many quests as you can and you'll be on your way to 50. By time you reach Velia you should have more than 10 if you do most of the tutorial quests.
Don't forget to use the conversation minigame to try and unlock additional quests from NPCs which can net you nice bonuses if you have spare Work Energy to use.