Slope is rise over run. For the first problem, you went down 8 and over 1 to your next point. Going down means you have a negative slope. -8/1 is 8. Your y intercept is where the line meets the y axis. The line meets the y axis at -4.
The line meets a new point every time it goes over 1 and up 2. Rise over run means 2/1. The line goes up so the slope is positive. The line meets the y axis at 3
