y-x=-2.
First draw the axes, y-axis is vertical and perpendicular to the horizontal x-axis. Mark off equal divisions on both axes where 0 is where the axes join. (Graph paper is usually clearly marked to make this easy.) Then, starting to the right of zero, mark 1, 2, 3, 4, 5 from left to right on the x-axis and similarly from bottom to top on the y-axis, starting above 0. You should have negative values, too: on the x-axis mark -1, -2, -3, -4, -5 from right to left starting from left of 0. Similarly mark the y-axis downward from 0. You're ready to draw the line.
You don't need the slope, because the intercepts will automatically make the correct slope. Now put y=0 in the equation: -x=-2, which is the same as x=2 so mark 2 on the x-axis (x-intercept). Next put x=0 in the equation: y=-2, so mark -2 (remember it's in the negative part of the axis) on the y-axis (this is the y-intercept).
You now have a point on each axis through which you can draw the line. Don't just join the points, draw the line to pass through the marked points. So the line will be inclined to the right. Every point on that line will satisfy the equation y-x=-2, and you can prove this by choosing an x value (for example, 3): go straight up from the x value on the x-axis till you meet the line then go horizontally towards the y-axis and note what value of y that is (in the example, you should find that y=1).