Hello welcome to careers360!

If you want to become a Mobile application developer the you might have interested in codig. So further after 12th take CSE or IT department in engineering and simultaneously you can learn Mobile application development ,web development,AI, machine learning etc..

So join in engg. And do anything that you are passionate about because a degree certificate is important.

If you are interested in mobile application development you need to know basics of Java.

There are some websites where you can learn from home itself. Here is the list of those websites you can go check over there

1. Nptel(courses are free and need to pay for certification exam)

2. Udemy

3. Edx

4. Courseera 

Hope this is helpful.

Good luck!