The answer to the above question is – every food scrap! We collect and compost fruit and veggie peels, coffee grinds, and any other food waste (which we conscientiously limit). Over time that compost becomes the fertilizer for our garden and nourishes our vegetable patch. We don’t use a composting machine or turn our compost, all we do is when it comes time to add more food scraps, we simply dig into the compost pile and hide the fresh waste inside the pile, this allows quicker compositing of the new food waste and also eliminates odors.
Garden compost heap
Large Compost Pile at the back of the garden 
Turning the soil of a veggie patch by mixing fresh compost
Kitchen compost bin
Compost bin under the sink 
Approx. one week’s worth of compost
Separating food waste from regular garbage for composting (whether you do the composting ourselves or the town does it for you) is perhaps the most crucial aspect of “recycling” because rotting food in landfills is a source of the powerful green-house gas Methane. Food scraps and yard waste together currently make up more than 30 percent of what we throw away, and could be composted instead.
Here is a good article from the EPA on the basics of compositing, what to compost and what not to compost etc.