How do I apply for 11th Grade in America?

So I'm currently In India but I was born in America so I am an American Citizen.
I've been studying outside America for almost 10 years now and I'm about to finish my 10th Grade.
After 10th I'm gonna go to America and start studying for my 11th grade. I just wanna know all the difficulties that can happen so I can start preparing to admit for the schools now as I will only be there by October ( Moms Visa stuff will only get ready by then...)
Will I be able to join school after October? How hard will it be? Should I start doing my admissions or whatever right now?

Did you are planing to attend public high school your residence/ address determines which school you will go to unless you are in a magnet program.
Google state/county/municipality for school districts, review the offered curriculum, contact admissions with your specific questions, find out what documentation you have to provide and what potential testing you may have to go through. Have mom join parent groups of the school district.

It isn't sure where we are staying as we are gonna stay in the place where my older brother gets accepted into college...
Is the admission process in most schools in America the same?

Pretty much the same with some local specifics.

I can only speak for New Mexico...but I would imagine your education is above New Mexico, if not USA standards....HOWEVER...I would begin the process as early a possible.  IF you know the state, city/town you will be  residing in, get ahold of the school system and ask for information and applications.  I wish you and your family luck in this endeavor.