Hello Chidambara Raju,the NDA exam is conducted by UPSC every year and you can prepare for the exam through various online resources and one of the best resource is,"Unacademy" app where you will get all the insights about the exam and you can listen to the great lectures given by aspirants who have cracked the exam.The pattern of the exam is,it has two papers... mathematics and general ability..The topics of both the papers include:

Mathematics: Trigonometry,algebra,calculus,vector algebra,matrices,geometry, statistics and probability.

General ability:This section contains both papers.,English and general knowledge.

General knowledge:physics,chemistry, geography,history,science,current events.

English:Vocabulary,error spotting,grammar and comprehension.

I hope this information is enough..If you have any more doubts,you are welcome to ask...