This tells us two things. Our slope is 3 and our y intercept is -4.
This tells us that we need to start at (0,-4).
Plot that point.
Since our slope is 3 (3/1), move up 3 and right 1.
This you will end up at point (1,-1).
Connect these two points in a straight line, and you have graphed your line.
It will look like this
