Step 1:
You can use papers with another color too, or draw a purple circle on a square paper yourself.
Mountain-fold over these two lines.

Step 8:
Repeat step 7 seven more times. The mountain-folds are already prefolded.

Step 6:
Prefold the model over these four lines.
Then turn the model.

DONE!

Step 12:
Hold the stem in your hand and pull the bottom edges outwards with your other hand.

Step 11:
This is a side view of the mushroom.
Press the top of the stem inwards, see arrows.

Step 10:
This is how the model looks from above.

Step 9:
Mountain-fold over these four lines.

Step 5:
Press these four spots flat.

Step 7:
Pull the spot indicated by the arrow upwards by folding over these two lines.
The line below is prefolded in step 6.

Step 3:
Turn the model.

Step 2:
Fold over these four lines.

Step 4:
Valley-fold over these four lines.

Joost Langeveld shows how to make the mushroom in this video (Joost is a popular You Tube artist):