Below is a sketch of a straight line with a gradient of m and a y-intercept equal to b. The gradient tells you that the line rises by m units as you run along to the right by 1 unit. The y intercept tells you where the line crosses the y-axis.
In the animations below, examine the effect different gradients and y -intercepts have on the graph of a straight line.
Notice the difference between lines with positive and negative gradients.