The value of m is the slope
If you have a equation like this:
y = 2x
2 is your slope. Your slope is always rise/run. This mean that for this equation you are going to rise 2 and run 1 since x is going to be equal to 1
The value of b is the y-intercept
For the equation above, you can see no b which means that you start at (0,0)
In this second equation:
y = x + 2
The b is equal to 2, so the y - intercept is 2 and you are going to start at the point (0,2)