Well, according to my own experience, junior high school mathematics learns numbers first-rational numbers, irrational numbers, real numbers, negative numbers, antonyms and so on.

Then there are formulas, numbers and formulas, quadratic roots, powers, cubic roots and so on. Then there are addition, subtraction, multiplication and division of numbers and formulas, factorization, inequalities and so on. . . .

Then there are probably linear functions, the concept and proof of congruent triangles, and so on. . . It seems that these are the first days. . . . . .

You can learn these first, well, if you want to continue to study in depth, you can watch some teaching videos of junior high school mathematics.

I hope the above will help you.