All you need is two pieces of paper and tape.
Step 1: Step 1: 1st Step
Tape the two pieces of paper together. It should look like this.
Step 2: Step 2: 2nd Step
Fold the top flaps into the middle and make sure there lined up.
Step 3: Step 3: 3rd Step
The picture explains it.
Step 4: Step 4: 4th Step
It should look like this.