What would you like to understand?

Once the full derivative curve is available, you select any desired $x$-coordinate within the visible window, look vertically up or down to intersect the orange parabolic graph, and interpret that exact vertical height as the slope of the tangent line to the original blue curve at that same $x$.

Conditions: The derivative curve spans the continuous plotting area.; Requires recognizing that the vertical position of the derivative graph encodes slope, not just the function output of $f$ itself.

Once the full derivative curve is available, you select any desired $x$-coordinate within the visible window, look vertically up or down to intersect the orange parabolic graph, and interpret that exact vertical height as the slope of the tangent line to the original blue curve at that same $x$.

Conditions: The derivative curve spans the continuous plotting area.; Requires recognizing that the vertical position of the derivative graph encodes slope, not just the function output of $f$ itself.