Calculus is the math of change. Derivative = rate of change. Integral = total accumulation. That's the whole concept.
Ask ten experts and you will get twelve answers. The underlying math, thankfully, only has one. Calculus is the math of change. Derivative = rate of change. Integral = total accumulation. That's the whole concept.
Slope of the curve at a point. Velocity from position, acceleration from velocity.
Area under the curve between two points. Distance from velocity, total cost from rate.
Derivatives and integrals are inverse operations. Beautiful and useful.
Do I need calculus for daily life? Rarely directly, but the intuition (marginal vs total) shows up everywhere in economics and finance.
What's a partial derivative? Derivative with respect to one variable, holding others fixed. Foundation of multivariable optimisation.
If you only remember one thing from this post, make it that the inputs matter more than the calculator.