At levels 3, 6 and 9 you can get skill cards, each having a different effect that can boost your skill.
Mirthwood: Skill Cards Guide
There are six skills in the game: Melee, Archery, Farming, Trades, Charisma, and Survival.
At levels 3, 6, and 9, you can unlock skill cards, each offering a unique effect to enhance your abilities. Depending on your focus-such as growing crops faster or selling them for more profit—you can select the card that best fits your strategy.
You can switch between skill cards at any time, but once changed, you won’t be able to switch again for 24 hours. If you have multiple skill cards equipped, you can change one slot per day.
To equip more than one skill card, you’ll need to unlock additional slots by visiting Fernfoot’s Place and spending your Fabled Feathers.