CDS exam is conducted under the Civil Service. the minimum qualification required is B.Sc. of a recognized University or equivalent with Physics and/or Mathematics as subjects or Bachelor of Engineering.
The exam takes place twice a year and the age limit is between 19-23 years.
CDS exam would include sections like :
English, General Knowledge, Elementary Mathematics, Mensuration, Geometry, Statistics. There are many reference texts that you may consider depending on your area of interest:
Asian CDS by R.P.Verma,
Referring to NCERT books shall also be of great help,
CDSE, Datason RP,
R.S.Agarwal for Arithematic
Arihant Publication for Reasoning and many more.