Those points you can see on the graph.
The first one refers to the x value and the second, to y value. If you notice, when you have x = 0, y = 3. When x = -5, y = 0.
When the line intercepts one of the axis, means the other coordinate is = 0.
3 is y intercept, it means the x value of that point is 0. The same happens to the x intercept - 5. It means the y value of that point is 0.
A ( -5 | 0 )
B ( 0 | 3 )
m = Delta y / Delta x.
Delta y is the variation over the x-axis. Delta x, the x axis.
Be safe!