Dear Deepa,
Combined Defence Service exam is conducted by UPSC twice every year for recruitment to office cadre of the Army, Navy and Air force. CDS exam is conducted generally in the months of May and October.
Candidates qualifying the written test are interviewed by the Service Selection Board and if finally selected, depending upon the choice given by the candidates and their merit list ranking, are sent to one of the following institutes for orientation training: -
(a) Indian Military Academy (IMA), Dehradun
(b) Naval Academy, Goa
(c) Air Force Academy, Begumpet, Hyderabad
(d) Officers Training Academy (OTA), Chennai