Mathematics can be learned just by having a questioning mind.
This display allows you to select a basic graph. It shows you two points on the graph, together with the line between them and a slope triangle for that line. When you drag the points so that they "crash", the line and the slope triangle may disappear. Begin to investigate that disappearance, and you are on your way to learning calculus.
Keep in mind: the points are actually taking small "steps" on your screen, and often avoid the "crash" by stepping over and around each other. Be patient!! For quicker examples, pick the bottom one on the list.