Instead of a solid mass, the inside kernels of the cocoa beans consist of tiny stems and unfurled leaves. After the beans are roasted, they are put through a winnowing machine which removes the outer husks or shells, leaving behind the kernels. Because they are not solid pieces, They break into smaller particles or sections call cocoa nibs which contain their inherent cocoa solids and cocoa butter (approximately 50%). This is the fundamental ingredients for making chocolate.
Cocoa butter is the natural fat found in cocoa beans (sort of like peanut butter). About 36% of the fat in the cocoa bean is "good fat": mono- or polyunsaturated fat and oleic acid (the fatty acid also abundant in olive oil). Of the saturated fat content in cocoa butter, over half comes from stearic acid. This saturated fat is not harmful for human body, because stearic acid have a neutral impact on blood cholesterol.
Cocoa solids is the nonfat component of chocolate. We can find this at grocery store sold as cocoa powder. Cocoa solid is the source of the aroma and flavours of chocolate.
Milling: After roasting and winnowing, the nibs are then ground into a thick liquid called chocolate liquor, which essentially is cocoa solids suspended in cocoa butter. Despite its name, chocolate liquor contains no alcohol.
Pressing: The processing now goes in a couple of different directions. Some batches of chocolate liquor are pressed to extract the cocoa butter, which leaves a solid mass behind that is pulverized into cocoa powder. The remaining cocoa butter is reserved to help in chocolate-making. Other batches of chocolate liquor are used directly to make chocolate.
First 1 minute 20 second of this video shows the process. Ignore the rest, it's confusing