I want to become Software engineer and would like to know what I should study?
Excellent choice. Software is a leading trend and i wish you all the best here.
On what you should study, for now stick to what is taught in School. When you progress to +1+2(or PUC), you will learn C and C++. Since software engineer is the field you are looking for try to understand the WHY's in programming. Try to explore languages like Python , Ruby etc. There is a concept called data structures- Learn and be good on this as you progress and you will be golden. :-)
During your next 2 years, choose science and mathematics as your subjects. Some schools also offer programming languages (C, C++) as additional subjects so you can opt for them as well. Please keep in mind if you want to go for a formal undergrad course in software engineering after your school, you would need to be prepared to meet eligibility criteria and also clear entrance exams of your choice of colleges. Mathematics and programming languages will help you to have an added advantage.
These days different schools and companies also organise programming competitions (Called Hackathons), you should start participating in these after you have learnt basic programming skills.
I would suggest you can study+1 and +2 in computer science, Science and Maths group to become software engineer.
1. Programming Languages (SQL, C, Python, Java, C#, etc.)
2. Data Structures
4. Database Design
5. Software Architecture/Design
6. Discrete Math
7. Linear Algebra
After your +12 graduation You can study bachelors in computer science Engineering, Information Science or BCA