The equations give you information as to where to plot points.
For y = -x + 1, you know the slope is -1, and the line intersects the y-axis at (0, 1). The y-axis is the vertical line; to plot (0, 1), find 1 on the vertical line and mark it. Now, the slope is -1; that means the line will slope downwards. To plot more points, count 1 unit down from (0, 1) and 1 unit to the right. You should end up at (1, 0).Connect those and you have a line.
For y = -2x + 4, the slope is -2 (so it will also slope downwards), and the y-intercept is 4. Find (0, 4) and plot it. The -2 tells you to count 2 units down (instead of 1 like we did for the last equation) and 1 over. That is the second line.
