To study astro physics, you first need to complete your class 12th with maths and other pure science subjects. If you have done that, here are the next steps-

• Get a astrophysics bachelor's degree. You can also get a bachelor's degree on any of the science subjects. 
• Finish a doctorate in astrophysics. 

You can include courses in astronomy, mathematics, computer science, physics and statistics to have a wider base of knowledge. 

Hello aspirant,

Some topics that you need to study for astrophysics are:

• The solar system
• Basic observation, system of measure and observation tools
• The nature of stars
• Late stages of stellar evolution and the end stages of stars
• Galaxies and cosmology

These are major topics which may include su topics like astronomic systems, constellation, etc.

Best of luck!!