Short answers, pulled from the story.
The Central Powers consisted of Germany, Austria-Hungary, the Ottoman Empire, and Bulgaria. These four nations sat between the Russian Empire to the east and France and the United Kingdom to the west.
Austria-Hungary declared war on Serbia on the 28th of July 1914. This declaration triggered a chain reaction that led to Germany entering the conflict shortly after.
The Central Powers mobilized over twenty-five million soldiers total across all member nations. Germany alone mobilized thirteen point two five million men while Austria-Hungary mobilized seven point eight million.
Cameroon existed as a German colony from 1884 until its complete occupation in 1915. Togoland became a German protectorate in 1884 but fell swiftly to Allied forces in 1915.
Bulgaria became the last member to join when it declared war on Serbia on the 14th of October 1915. Its late entry transformed the Quadruple Alliance into a more complex military coalition facing the Triple Entente.