Short answers, pulled from the story.
Colonel Draža Mihailović led the Chetnik movement into the hills of Ravna Gora on the 6th of April 1941. He started with a small group of seven officers and 27 other ranks to form the Ravna Gora Movement. This group became formally known as the Chetnik Detachments of the Yugoslav Army.
Stevan Moljević wrote a memorandum titled Homogeneous Serbia in June 1941 advocating for a state including 65 to 70 percent of the total Yugoslav territory and population. The plan envisioned the expulsion of 2,675,000 people from Greater Serbia including 1,000,000 Croats and 500,000 Germans. Mihailović endorsed these proposals in a set of detailed instructions dated the 20th of December 1941.
The Chetniks collaborated with Axis forces following the massacres in Kraljevo and Kragujevac in October 1941 where over 4,500 civilians were killed. Mihailović concluded that killing German troops would result in further unnecessary deaths of tens of thousands of Serbs. This led to a policy of using the enemy and operating as legalized auxiliary forces under Axis control.
Estimates of the number of deaths caused by the Chetniks in Croatia and Bosnia and Herzegovina range from 50,000 to 68,000. More than 5,000 victims are registered in the region of Sandžak alone. About 300 villages and small towns were destroyed along with a large number of mosques and Catholic churches.
An agreement was concluded on the 11th of January 1942 between the representative of the Italian 2nd Army Captain Angelo De Matteis and the Chetnik representative for southeastern Bosnia Mutimir Petković. This agreement stipulated that the Italians would support Chetnik formations with arms and provisions. In 1942 and 1943 an overwhelming proportion of Chetnik forces in Italian-controlled areas were organized as Italian auxiliary forces.
In early May 1945 Chetnik forces withdrew through Ustaše-held Zagreb and many were later killed by the Partisans as part of the Bleiburg repatriations. Pavle Đurišić had negotiated an agreement with the Ustaše in March 1945 to provide safe conduct for his Chetniks across the Independent State of Croatia. The movement faced a catastrophic collapse with their forces retreating through Ustaše-held territory to Austria and Italy.