As part of the greater Nazi effort to exterminate the Jews of Europe, the Treblinka concentration camp was second only the the more famous Auschwitz-Birkenau in terms of deadliness. With thousands of cattle cars stocked to the gills with Polish Jews converging on it day after day for months on end, its facilities orchestrated the annihilation of at least 800,000 of them, and quite likely more. All this we know from what remains of eyewitness testimony and physical evidence despite Nazi efforts to destroy both, and most especially train schedules whose 'final destination' declarations take on a macabre connotation with the understanding of what really occurred at the end of the line.
Massive and systematic executions at the Treblinka camp fell under the aegis of Aktion Reinhard (alternatively Einsatz Reinhard and Aktion Reinhardt), a facet of the "Final Solution of the Jewish Question" (Endlösung der Judenfrage) devoted to physically exterminating the Jews of the Generalgouvernement of former Poland.
A article by Stephen Potyondi at the Holocaust History project demonstrates the evil purpose of the Treblinka death camp.