First of all, we have to draw the line. To draw a line, we only need two points. To sample to points, we choose two arbitrary x values, and compute the correspondent y values.
We may choose x=0 and x=3 to make computation/drawing easier. We have


So, this line passes through the points (0, -6) and (3, -5). Draw these two points and connect them: you have the line

Now, to solve the inequality

recall that smaller values for y means "below" in the coordinate axes. So, every point that lies below the line is a solution to the inequality.