<<Graphics`Spline`

Here is a list of points.  We then plot them.

pts =
  {{0, 0}, {1, 0.5}, {2, 3}, {3, 1}, {4, 0}, {5.1, 2.4}};  ptss = Map[Point,pts];
  Show[Graphics[{Hue[0.05], PointSize[0.02], ptss}]];

This is a graph of the cubic Spline primitive combined with other primitives. Here a blue line  connects the points making up the spline.  The spline is shown in gray.

Show[Graphics[{Hue[.17],Rectangle[{0,0},{5.1,3}]}], Graphics[{Hue[0.4],
    Map[Line,{{{0,0},{0,3}},{{1,0},{1,3}},{{2,0},{2,3}},{{3,0},{3,3}},{{4,
            0},{4,3}},{{5.1`,0},{5.1`,3}}}]}],
  Graphics[{ Hue[0.6], Line[pts], ptss, GrayLevel[0],
    Spline[pts, Cubic]}],  Graphics[{Hue[0.05], PointSize[0.02], ptss}],
    PlotRange -> All]