Simple instructions are included on the printable, but I've included more detailed instructions on this post, as well. It's not required, but I would recommend printing out the Jack-in-the-box on card stock to make it more sturdy.
Cut out and fold Jack on the dotted lines, accordion style. Make sure to start the fold underneath Jack. The first fold needs to be folded behind him.
When folding the box, fold inward at each dotted line.
Next tape the two tabs underneath both green squares together.
Add a strip of tape to the bottom tab of the folded Jack, and tape to the bottom of the inside of the box.
Then add a strip of tape to the small tab on the side of the red box and fold inward. Tape to the inside of the box.
Finally, add one more tape strip to secure the bottom two tabs underneath the box.
Fun, right? Mac begged me for days to make this. He and I both made a Jack-in-the-box. And then he stole mine. He really did.