Here is how I do it.
List of things needed:
1/2 gallon plastic juice jug, it's important that it is clean use some near boiling water to rinse it out well. I use these because they are more stable than 2L bottles.
Airline tubing
Check valve
Yeast
Sugar
Measuring cup and spoons
Some sort of diffuser (glass diffuser, airstone, plumbed into a misting system etc).
A drill or some way to make a hole in the plastic cap
Optional - Baking soda to help keep the solution from getting too acidic like i said optional
Now that you have your supplies together it's time to get working on making the container. Start by drilling a hole in the container cap that is just smaller than the outside diameter of the airline you are using. If you make it small enough you will get an air tight seal.
Now once you get the hole drilled out you want to put the airline through the cap. This step should be the hardest part of it all as you need to make sure the hole is hard to get the hose through, to help with this step you can cut airline at an angle so you can put the pointed end through first and grab it or use some pliers to help as well.
Next step is to connect your check valve.
Then you want to connect your diffuser to the airline.
Now make up your mix of yeast, sugar, baking soda (optional), and tepid water. What I use is about 1 1/2 cup- 2 cups sugar, this goes in first. Then I fill the bottle with tepid water to where the bottle starts to narrow, note I marked the bottle in the picture for you with a green sharpie. Optional add 1/2 teaspoon of baking soda. Finally add 1/2 teaspoon of yeast.
Finally you put the diffuser into the tank and wait for the yeast to start producing co2 should take about 30 to a couple hours depending on the temp of the water. If you use to hot of water you will kill the yeast. Make sure to check for any leaks if you don't see any bubbles as well. Check connections at the check valve and especially at the cap where it connects to the bottle and the hole you made.
That's it this mix should last you about 2-3 weeks of good production then taper. It will start off really vigorous then taper off and stabilize in a day or so and be pretty consistent for the next couple of weeks.