Step 1:
I glued three white a4-size papers together into one long rectangle.
(You can also use two layers of paper to make a stronger curtain rod).
Fold in half

Step 5:
I used three small black nails to attach the curtain rod to the closet, one in the middle and one on each end.

Step 3:
The curtain rod should be strong enough by now, fold it in half one more time to be sure it's strong enough to hold a curtain.

Step 2:
Fold in half two more times

Step 4:
Ready.....

Done!