Step 1:
Glue two paper squares together or fold (and cut) a large square in half.
Fold over this line.

Step 8:
Press open, see arrow

Step 6:
Prefold

Step 11:
Repeat step 9 and 10 op the other 4 edges, they're next to the previous 4 edges.

Step 10:
Repeat step 9 on the other three same edges

Step 9:
Pull the upper edge outwards and fold over these two lines. The left line is a little curved and the right line is a prefolded line.

Step 5:
Prefold.

Step 7:
Glue both ends together.

Step 3:
Fold both edges to the centerline and unfold the model.

Step 2:
Prefold in half.

Step 4:
Fold over the left line. And fold the three edges to the right.

Step 12:
Pull the upper edge a little further outwards.

Step 13:
Fold downwards, see arrow

Step 14:
Repeat step 13 on the other three edges.

Step 15:
Make sharper folding lines at the bottom of the vase.

Done!
I filled the vase with small pebbles, for decoration and preventing from falling.