What is Compost ?

All vegetable waste will rot down eventually. A compost heap creates a natural environment where this process can be accelerated, resulting in a  material rich in nutrients and humus.
To encourage a strong population of micro-organisms they must have favourable conditions - i.e. Air, Food, Heat, and Moisture. Your compost heap must therefore be constructed in a way which allows these requirements.
Throwing away refuse which can make compost is wasteful. Lawn cuttings, weeds, vegetable peelings / stems and dead leaves, ( newspaper, waste paper/card and cardboard but not too much; should all be torn up or crumpled and mixed in with the rest of the compost), can all be used to make a rich, healthy fertiliser, and soil conditioner for the garden, and its free.

Improving your Compost

You should compost things with a range of textures; you need a mix of soft waste material as well as coarser rougher stuff. This helps to aerate the compost. 

Mixing and turning the compost helps to introduce and maintain oxygen into the compost; this helps the organic matter decompose faster. 
Grass cuttings can be composted but you should not put thick layers in the compost bin without mixing other, coarser materials in with the grass to get oxygen into the mixture. Grass cuttings in large quantities will compact and form a thatch, restricting air flow and slowing down decomposition of the grass as well as other waste. 

The compost in the container should be moist, but not too wet. Wet any dry material which you add to the heap and water the heap in dry periods of summer - but protect from excessive rain. Rain will drain the nutrients away, e.g. nitrogen and phosphates. 
Organic waste turns into compost faster if it's warm. Positioning your compost where it gets some sunshine is beneficial; if it's in full sun this may dry out the compost too much. 

Use different materials as large amounts of one substance tend to give an 'unbalanced' diet for micro-organisms

The compost heap must have air. slatted sides allows air to filter in higher up. 

A healthy compost heap should reach temperatures of 140 degrees Fahrenheit (60 degrees Celsius) at centre, and this heat will kill weed seeds and sterilise your compost. However to maintain a good temperature in periods of cold and therefore sustain the process at work you should insulate your heap, but don't completely block the airflow.

The correct ratio of carbon and nitrogen must be maintained in the heap. Many plants (particularly older ones) have a lot of carbon in them and micro-organisms need nitrogen to break it down. This can be added in many forms as an 'activator' layer when you build your compost heap. Animal manure (horse, pig, poultry), bone and fish meal and manufactured products (e.g. from seaweed) make excellent activators. If you have acid material in the heap add a  layer of lime to can help neutralise.

Some gardeners add layers of garden soil to the heap but don't overdo it. Other high Nitrogen additives are layers of nettles or comfrey.

If you can, build three compost boxes next to each other, always leaving one vacant, empty one into the vacant box every 4 to 6 weeks, this aerates and mixes the heap enabling all materials to rot properly.

In the summer, compost should take as little as 6 months to make, but in winter it takes longer. A mature compost should be dark brown and should smell like good soil.

You can use your compost in a number of ways. If you want to use it to feed your plants put it around them in spring when plants are beginning to grow. To use the compost as a soil conditioner put it on in the autumn so that the soil is protected through the winter.