Step 1:
Prefold in half.

Step 8:
Valley-fold this prefolded line into the right direction.

Step 6:
Fold both parts in half

Step 13:
Tape or glue these edges together

Step 12:
Fold the line indicated by the large arrow to the line indicated by the small arrow.

Step 11:
Fold the line indicated by the large arrow to the line indicated by the small arrow.

Step 10:
Fold the line indicated by the large arrow to the line indicated by the small arrow.

Step 9:
Fold the line indicated by the large arrow to the line indicated by the small arrow.

Step 5:
Fold the edges to the centerline.
Then unfold the line on the right.

Step 7:
Open the model, see arrows

Step 3:
Fold the edge to the folding line of step 2.
Then turn the model.

Step 2:
Prefold the edge to the centerline.

Step 4:
Prefold in half over this line

Step 14:
Use tape or glue to close the top of the block

Done!

In this video Joost Langeveld shows how to fold the domino blocks: