It depends on the size of the canister...
If you have the Nutrafin Natural Plant System canister, fill with sugar to the top of the bottom fin that is sticking out from the side. Then fill it with lukewarm water to the top of the upper fin sticking out from the inside. Drop in 1/4 - 1/2 teaspoon of yeast and stir it up, cap it, hook it up and it should start producing bubbles within the hour. Here is a DIY version that I've used in the past and that worked well for me. Can't recall which forum I pulled it from though. The spelling could use some help, but here is the quote:
"first get an empty 2 liter pop bottel. than take the lid and make a hole in the lid big enough to put air line tubing in. i use a nail heated in a candel or gas burner to do this. next thread enough air line tubing to reach your take from were the bottal will sit in to your tank. although regular air line tubing will work for a while, CO2 has a corosive property that dissolves the airline tubing to a point where it leaks. if you can find it us CO2 resitant. it is a little more expensive but it will save you the head ache later. use a hot glue gun or silicon rubber to seal the gap between the cap and the tubing. next take the bottal and put 2 cups of granulated (table) suger in. after that fill it with luke warm tap water till it is at the part where the bottle starts to bend at the top. next take 1/2 tee spoon yeast and pour that in. if you live in an area that has very soft water, add a 1/4 teespoon of bakeing soda to prevent the mix from becomeing too acidic. attach the cap/tubing to the bottal, hook an air stone to the end and your ready to go. CO2 should start to come out the end in 1-24 hours."
