Dig a hole sufficient enough to bury a significant amount of trash. The system will not return the investment if the amount of trash is not large enough to biodegrade for several years. The specifics depend on your particular configuration and costs.
Insert vertical lengths of plastic perforated pipe into the hole, and connect those pipes to a central collection pipe. The perforated pipe will collect methane --- a gas produced as the end stage of digestion by a series of bacteria.
Fill the hole with trash. The higher the organic content, the greater the amount of methane that will be produced.
Cap the hole with well-tamped dirt. The dirt prevents the methane from bypassing your collection system and escaping into the air.
Connect the collection pipe to the input of a methane-compatible turbine.