Anyway...you are going to need an old pair of kitchen shears. I keep a pair around just for the purpose of cutting thick cardboard and metal. Soda cans are your next item. Be sure to wash them out. I recommend letting them dry a bit too, or you may spill water all over your work space. Take a dry can and carefully cut a slit into it.
Now for the next part, you need to be VERY careful. The edge is a bit jagged you don't want to cut yourself. Also, as you cut, try to make slow, even cuts. This way, you reduce the chance of having metal shavings fall off. Insert your scissors into the slit and carefully cut the top off the can. You can use one hand to depress part of the can as you go, allowing the scissors to fit in the slit and cut more evenly.
Now that the top is off, cut a slit down one side toward the bottom. This will allow you to more easily cut and remove the bottom of the can.
Don't forget...if you have something green to share, pop over to Scrap Our Stash.