Number and Algebra comes first for most students. It covers arithmetic and geometric sequences and series, sigma notation, the binomial theorem for positive integers, laws of exponents and logarithms, and proof techniques. These are the algebra skills you will use again in every other topic. Weakness here tends to show up later.
Functions builds on that base. You study domain, range, inverse and composite functions, graph transformations, quadratic and rational functions, and exponential and logarithmic models. You also learn to choose a suitable function for a real situation and interpret it. Geometry and Trigonometry then adds spatial and periodic ideas, and Statistics and Probability develops analysis and modelling.
Calculus ties the earlier work together. Understanding how a function behaves near asymptotes, intercepts and turning points helps you sketch curves and reason about tangents. If your algebra is secure and your function sense is good, calculus feels like a natural next step. If not, it is worth going back and repairing the base first.