Skills can be trained by various actions that relate to the skill. Performing any of these various actions grants the player experience in that skill.
There are currenty 17 Skills in Gran Skrea Online.
Combat skills like Light Armor only gain experience if you get hit during combat and killing the monster within the next 30 seconds after the last hit you took.
All skills that you need to survive the harsh nature and furious monsters in Gran Skrea can be found here:
All skills surrounding your daily life and support you in battle, no matter if brewing some potions, gathering and cooking food or setting your sails for adventures, can be found here.