I learned about hugelkultur, a german word meaning "mound culture", in Toby Hemenway's book "Gaia's Garden: A Guide to Home-scale Permaculture."
Hugelkultur involves burying dampened logs, branches and twigs underneath layers of compostable materials, leaves, finished compost and topsoil. The resulting mound can be planted directly into.
This method offers several benefits. The wood holds a lot of moisture, accessible to plant roots for long periods of time, thus watering will be required less frequently. The logs, branches and layers of compostable materials offer habitat for soil organisms, and the slow decomposition of the wood will create healthy and fertile soil. It is a version of composting in place (like sheet mulch).
It is important to include nitrogen rich materials in the layers on top of the logs, and shoved inbetween them, since the decomposition of the woody materials will use a lot of nitrogen in the process. A good carbon/nitrogen balance can be maintained by including nitrogen rich kitchen scraps, fresh leaves, etc into the mound's layers. Also planting nitrogen fixing legumes (peas, beans) in the hugelkultur bed will also add nitrogen into the soil.
I decided to try it out in a specific area of my backyard garden. I placed the mound in front of a south facing fence. The hugelkultur bed will serve many purposes here. It will allow me to grow climbing varieties of plants up trellises along the fence, some of which prefer to be grown in mounds (winter squash). It will provide long term fertility to the soil in this area of the garden as the logs and branches decompose. It will improve water retention in the soil in this area. It's physical location allows the mound to act as a physical barrier preventing soil and water runoff into my neighbors backyard, due to the existing slope in that direction.
This is a good example of the permaculture principle of stacking functions - getting many yields from one element of the garden system. The hugelkultur mound provides space to grow climbing and mound varieties of vegetables by providing a niche for them, it enhances the main space in my yard where I can garden vertically, it improves water retention, soil quality, and prevents erosion. It will serve multiple functions in my garden.