and which type of preparation i have to do for CAT & Which month the examination of CAT held every year

CAT has 3 sections - quants, verbal and LRDI. for self preparation, use Trishna for quants, Nishit K Sinha for LRDI and arun sharma for verbal. if you want, join TIME or IMS for best preparation. generally the exam is conducted in a 20 days online format towards the end of november.