Question in Coordinate Geometry

hey people,

Im about to complete week two of 2 month prep. I had a little doubt in Coordinate geometry before I move onto to geometry. I see Greg using y=mx+b to draw the lines. My question is, How do we find out slope i.e. rise/run and implement in the above formula? Secondly, how to we plot that line using this info? Please explain this in very easy and step by step method. Thanks in Advance!!

m is the slope

Find two points that lie on the line (i.e., satisfy the equation y = mx + b), and then sketch the line passing through both points.