Hi Manish!
You have made a good decision by choosing to write NDA. Now, you need to know that the NDA exam is conducted twice every year. The first exam is conducted in the month of April and this exam is called NDA-1, whereas, the second exam is conducted in the month of September and this exam is called NDA-2. They are named so only to prevent any misunderstandings. For the syllabus and all other information regarding this exam, you can refer to the following official link, which opens up the pdf you require:

https://upsc.gov.in/sites/default/files/Notice-NDA-I-2019-Engl.pdf

The syllabus starts on page number 17. After referring to the pdf, if you still have any doubts, please feel free to comment.

Let me know if this answer was helpful and all the best for your future!