Compute $\Delta y$ (up or down) and $\Delta x$ (left or right) between those two points.

Write the slope as $\dfrac{\Delta y}{\Delta x}$ and reduce the fraction to lowest terms.

In Desmos, type the points $(2,1)$ and $(8,5)$ as separate expressions to show them.

Type the expression $(5-1)/(8-2)$.

Desmos will display the simplified value of the expression; that value is the slope of the line through the two plotted points.

Use the two marked points on the graph: $(2,1)$ and $(8,5)$.

Compute the change in $y$ and the change in $x$:

So the slope is $\dfrac{4}{6}$.

Simplify $\dfrac{4}{6}$ to get $\dfrac{2}{3}$.

Therefore, the slope is $\dfrac{2}{3}$.