Y = mx + b is the equation for a straight line. "B" is the point value of where the line intercepts the y axis, called the y intercept. "M" is the value of the slope of the line. "X" is the value where the line intercepts the x axis.
The y intercept is found by examining where the line intercepts the y axis. The slope of the line is found by dividing the change in "y" values by the change in "x" values. Another way slope is described is "rise over run." This version of an equation of a straight line is also referred to as the "slope-intercept" form.