If you haven't noticed, you use the basics taught in elementary to learn more advanced concepts taught in middle schools, and then you use the more advanced concepts to learn more in high school. It all builds upon itself.
You must learn how to add, subract, multiply, and divide before you try to start more davnced algebra. You can then use this advanced algebra to aid in the learning of basic calculus concepts such as limits, derivatives, and integrals, and then you can use that for more advanced calculus concepts such as double and triple integrals, or for solving differential equations. It is all equally important as to learn more, you must know more.