Dear aspirant hope you are doing well..

Yes you can join NDA in army wing only if you have maths in your subjects then you can also join Navy but not the Airforce wing..

Preparation tips for NDA exam

Go through the syllabus of NDA Syllabus

https://competition.careers360.com/articles/nda-syllabus/amp

Make a time table..

Make short notes of important topic.

Practice previous years question paper..

https://competition.careers360.com/articles/nda-question-papers/amp

Do revision on regular basis.

For more details click on the link below

https://competition.careers360.com/articles/how-to-prepare-for-nda

hope it's helpful

thank you