Greetings candidate 

NDA National defence academy is situated in Pune. It is a national level exam organised by the UPSC Union public service commission to recruit candidates for tri services mainly Army, Navy, Air force. It is conducted in 2 phases which is followed by ssb INTERVIEW. NDA is conducted twice a year in the month of April and November. The exam is conducted offline mode. 

Following is the eligibility for educational qualifications - 

For Army wing - 

Candidates must have passed 12th to be eligible to apply for nda. 

For air force and navy - 

Candidates must have passed 12th class with physics and maths as subjects 

Exam pattern - 

Mathematics - 

Total question's - 120 

Total marks - 300

General ability test - 

This section contains 2 sections mainly English and general knowledge. 

Total questions - 150 

Total marks - 600, English - 200 and gk - 400

The gk section has following topics covered - 

Physics chemistry 

General sciences 

History 

Geography 

Current affairs 

So since you are aware of the exam pattern and topics following are some of the important websites for mock tests where you can go and practise - 

Tcyonline 

Aglasem

Prep. Youth4work

Testbag

Apart from this you can check youtube as it is one of the best and free learning sources to prepare for the exam

Just search for the topics you are looking for and you will get various videos on that. 

I can tell you some channels which have large videos on various topics - 

Studyiq for gk and current affairs 

Takshizila for maths 

WiFi study

Adda 247 for English 

I hope the answer helps. Thank you