Harvesting mushrooms is done using a shovel. There are several types of mushrooms in the forest, the entrance to it found in the back of the campus between the sanctuary and the student houses. You can harvest a mushroom by aiming yourself towards it, digging with your shovel, and you will harvest it in to your inventory provided it isn't moldy.
Aratz are a very plain looking brown mushroom. Their smooth dome shape gives them away and small size by comparison sets them apart from the rest.
Kamenas are mushrooms with a very saucer like shape. They are white/tan at the bottom of the shape, have a blue stripe in the middle, and then brown at the top. They can grow to be rather large when fully grown.
A Letjza is a tall brown and white pointy mushroom.
Siloza is a mushroom that grows on tree stumps. It is white in color and has a thin stipe.
Tzenk is a rare mushroom that resembles a small yellow flower in its shape.
Ekar is a mushroom of small size with an overflow from light green to purple. The cap has a shape as if it flows.
Alanarh is a rare large mushroom with a black cap and a white stipe with red spots.