You put the stuff that you want to compost on the top (the lid is opened in this picture) and you stir it around occasionally to keep it aerated. The soil settles to the bottom. The door on the bottom slides up so you can take out a little if you need it. If you need a lot more, you can also take the entire unit apart and take out the soil that you need and then return the parts that are still composting.
I opened the top - half expecting a raccoon or something to yap at me - and noticed that it was mostly filled with twigs, or "yard browns" as the website calls them. There is some soil on the bottom. I think that I will add that soil to my pots that I'm saving for the tomatoes. I could also throw it on the parts of the garden plot where I have not planted anything yet.