There are many of these types of tutorials, but none that I could find that instructed you to keep the bottom of the bottle on and not cut it off completely.
Keeping the bottom on allows you to turn the bottle over without spilling your soil.
Step 1: Materials: Upside Down Tomato Hanger
Empty two liter bottle
Knife and/or scissors
Step 2: Cut the Bottom of the Bottle.
Using a knife, cut the bottom of the empty bottle, leaving about an inch uncut so that the bottom remains attached.
Step 3: Fill the Bottle With Soil.
Step 4: Close the Bottom, and Turn the Bottle Over.
Step 5: Put Tomato Plant in Bottle.
Cut off a couple of stems so the tomato plant will grow new roots and poke the tomato plant deep into the neck of the bottle.
Turn bottle over.
Step 6: Attach Twine. Hang.
Poke two holes in the bottle with your knife and pull the twine through.