The slope on a graph is "rise over run" (rise/run)
The equation for slope is mx + b = y. (the mx is the slope)
To find the slope, you will see two points on your graph. From one point, count either upwards or downwards from the y axis till you reach to where the other point is. (this is the rise)
After finding the rise, you will then count either left or right across the x axis till you count to the other point.
For example, if you had one point at (-3,4) and another at (6,2)
The rise would be 6, and the run would be 6 as well.
hope this helps