I’m not exactly sure what part you’re confused about so I’ll explain this problem for you. The first step would be knowing what slope intercept form is; y=mx+b. Knowing this, our first step (the easiest one) would be to find “b” also known as the y intercept, all you need to do is find where the slope crosses on the y axis. In your case, this is at the point (0,-6) so b (the y intercept) would be -6. Now for the next step you need to find the next point (from the y intercept -6) where the slope intercepts the y axis (this is always going to be left of the y intercept). So if you look closely, the next point the slope intercepts is (5,-8) which will now become our “m” in the equation. Finally all we need to do is plug them in slope form. The final answer will be y=-5/8x-6
If you have any further questions; or if I didn’t clear your confusion please don’t hesitate to reply to this answer. I’ll be more than happy to further assist you!