This is so easy, it's not even funny!
Step 1: The tube
roll a piece of paper to a marshmallow sized tube. USE PRINTER PAPER!
Step 2: Taping The tube
Tape both ends & the middle.
Step 3: Firing
Put a marshmallow in the tube & blow
Step 4: A tip to firing
If you put the mallow in your mouth & fire it, it will stick. That's good!
Step 5: Last step