Cocoa powder is obtained from processed cocoa beans. The beans are ground to produce chocolate liquor, which is pressed to extract cocoa butter. The paste left behind from the pressing is ground and sifted into cocoa powder.
When a recipe on this site calls for cocoa powder, always use the best-quality cocoa powder, preferably Dutch-processed, but natural cocoa works as well.
Dutch-type cocoa has been treated with alkali to make it taste less bitter than natural cocoa.
Never replace real cocoa powder with sweetened cocoa drink mixes etc. Those are not intended
for baking (and have no resemblance to real chocolate or cocoa taste anyway, no matter how they are used).