Hello Rajibul ,

NIOS (National Institute of Open Schooling) is an institution and a recognised board of education in India which is run by the National Open School Society under the Ministry of HRD, Government of India. This Board was known as National Open School (NOS) earlier.

The key purpose of NIOS is to provide primary, secondary, senior secondary, vocational, and life skill education to a diverse group of learners which include differently or specially enabled students.

From the following link, you will get all the needed information about NIOS process

https://nios.ac.in/student-information-section/admission-procedure.aspx

Hope this helps