u plot the 2 points on the computer where (x,y), for you put a point on where x=4 and y=0 for (4,0) and do the same for the other one and it makes a line so just trave it (not sure how your website works lol)
to find the equation, y=mx+c u need a gradient and a constant so u find the gradient first by taking (5-0)/(8-4)=5/4=1.25
u see where the y-intercept is in the graph above that you made, that will be the constant
so u put the constant and gradient in your eqn and u get the answet
