As we all know that Biogas typically refers to a gas produced by the breakdown of organic matter in the absence of oxygen,

"Biogas is produced by the anaerobic digestion or fermentation of biodegradable materials such as manure, sewage, municipal waste, green waste, plant material, and crops, Biogas comprises primarily methane (CH4) and carbon dioxide (CO2) and may have small amounts of hydrogen sulphide (H2S), moisture and siloxanes.

The gases methane, hydrogen, and carbon monoxide (CO) can be combusted or oxidized with oxygen. This energy release allows biogas to be used as a fuel"

True but this is the definition of Wikipedia not mine....

The working portion made simple is that by putting all your kitchen wastes and vegetable wastes (avoiding onion peels, lemon, orange waste, egg shells and bones in the meat...and other non degradable objects) in the biogas plant gives you ample energy.

For the starters we use cow dung (around 20 buckets of them) diluted with water (cow dung have millions of small bacterias in them), we have to cultivate these bacteria inside the plant by giving them the waste food, as a result their excreta which I believe is used for cooking. We have to take care in not killing the bacteria by avoiding the above said materials.

After installing your plant you have to wait for 10-15 days to let the gas fill your tank. After that you can connect it to your stove (Specially designed for the Biogas plant, provided with it) as the methane gas is heavier than the LPG, and moreover it’s not in the form of Liquid, so it cannot come out the normal gas stove. Another good part of this gas is there’s no danger in it if it’s left open. Only loss is the gas you loose. 

After you start using your gas plant you will get around 15-20 minutes of gas. For that you have to put around 2 kg of waste and 2 liters of water. (The water you get after washing your rice or left over water of cleansing fish or meat, the water we get after the rice is cooked can also be used don’t use plain water with the waste). In waste you can include leftover vegetables, leftover food, fish or meat waste etc. continue this for two weeks after two weeks slowly increase the waste by half a kg say 2 ½ kg of waste and 2 ½ liters of water. Another two weeks and another increase.

Likewise you can reach a level of 7 kg’s of waste and 7 liters of waste water, upon reaching this we can get a minimum of 3 hour of continuous gas.

At present I am getting 4 hours of gas 1½ hour in the morning, 1½ hours in the noon and another hour in the night. That’s my experience.

One thing you have to keep in mind is never increase the waste suddenly. If you have a party or function in your house or neighbor, you’ll have more waste, I say you store it another closed plastic container. You can also collect the extra waste in the container, allow the waste to decay there for a day and then put the waste, this way of storing-decaying process I have noticed a great speed in converting the waste into gas.

There is an outlet from where the remains of waste put in the plant comes out in the form of slurry. The amount of waste you put in the plant is the same amount of slurry which comes out, that is another reason why you should not put more waste suddenly, this way more bacteria goes out and your remaining bacterias will suffer doing over load of work, which in result will low your production.

This slurry is a great insecticide and fertilizer.

Dilute a quantity of slurry thrice and you can spray it on you plants, a good organic insecticide against pests.

Dilute it twice to water your crop a great organic fertilizer for you plants.