How to study astronomy at home?

Go outside. Look up. Learn to recognize the bright stars, what constellations they are in and where to find them in the sky. Notice that big shiny thing called the moon. Don't forget there is another thing called "the sun" up in the sky during the day. Think about what you are looking at.

If you are interested in learning more, get yourself a few textbooks that will explain it all. Old second hand textbooks are ideal because they are cheap and the basics of astronomy have not changed in half a century. Don't neglect learning about the history of astronomy. There are plenty of lessons to learn from it.

Forget the physics and math unless that is the direction you really want to go in.

Steps to undertake to study astronomy at home:

1)  Wait for night time

2)  Go outside

3)  Look up

4)  Repeat as needed

Instead of worrying about high school stuff, just study things that you can understand. If one textbook is too easy, then go up a step. If it’s too hard, then go down a step.

As I gather, you are a youngster in 4th grade so about 9 or ten years old. I wouldn't worry as of now about what you should study to have a good knowledge on astronomy in later years. Science classes in schools actually give you the startup. My granddaughter, who is 11 now, learned in her science class several things regarding astronomy. For instance, her class learned what a light year is and its distance.

Be attentive during your science hours and if something is not quite clear to you, don't hesitate to ask your teacher to explain it with simpler words. Meanwhile, there is a good choice of astronomy books for children that you can leaf through. This will boost your knowledge and somehow prepare you in a better way to study astronomy as an adult in college.

Look at the sky through binoculars or a telescope.  Learn the positions of the stars and planets and the coordinate systems for locating them.  Note the magnitudes and colours of the stars and the movements of the planets.  And so on.