Open Desmos
Plot the two points on the graph
Use the distance formula: (d=sqrt{(x_2-x_1)^2+(y_2-y_1)^2})
Enter the formula in a Desmos expression line
Replace (x_1, y_1, x_2, y_2) with the coordinates of the two points
Read the distance shown by Desmos
Use the distance tool if available in your Desmos version
Click the two points to measure the distance directly