Step 1:
Take a standard printer- / copy paper.
Fold in half.

Step 8:
Repeat step 7 on the other side, see arrow.

Step 6:
Fold both corners inwards over the prefolded lines (Make the same folds (=valley-folds) on the backside).
Glue / tape the edges together.

Step 9:
This is how the bottom of the vase looks.

Step 5:
Prefold.

Step 7:
Fold the edge downwards over the blue prefolded line

Step 3:
Fold over this line.

Step 2:
Prefold.

Step 4:
Fold the left edge under the flap on the right.
Glue / tape both edges together.

Done!