The walking is extremely slow and the mouse sensitivity is crazily high.
But I like the overall feel of the game.
I don't understand how to proceed. after having built the pickaxe and the strange stone thing
Thanks for the feedback! The walking speed and mouse sense are definitely things I was unsure about.
To proceed from where I think you are, you need to find the cave near the forest with the big wooden board over it (you should be able to year a bell ringing to indicate where it is). You can chop down the board and inside is the fairy which will help you open the door on the upper level where you'll find the final puzzle of the game where you will use the stone weight. :)
I hope that helps and thanks for playing!