Experiment with ingredients and discover new ways to make potions, since each potion is the result of specific combinations of elements, what you will need is to mix herbs in the correct way and not necessarily a recipe.
Rediscover potions forgotten in time through an old map showing where the knowledge of each forgotten potion is kept.
There is a problem, the valley has changed and the map is no longer very reliable, so use the libraries in each town to find information about this forgotten civilization and tales of local mysteries, to reach such places deep in the forest and recover the knowledge lost from them.
Use mushrooms, flowers, roots and herbs gathered in the woods to make magic potions.
Learn the art of potion making with the cauldron and use the two other tools you will unlock during your adventure, to make increasingly advanced potions.
To explore the valley you need to fund your travels, and what better way to get that than to sell the potions you make to potion stores.