This post shows you how to draw a closed polygon (in this case a triangle for simplicity) on a 2D scatter plot in Excel 2003.
1. For this you need to sketch what you want to draw on a paper or just create a mental visualization.
2. In this sketch you need to define the vertices (corners) of the shape and figure out the approximate coordinates.
3. Create a table in excel with these coordinates (in the proper sequence) not forgetting to start in one point and return to the same point (A to B to C and return to A in order to close the loop).
The following picture is a thumbnail of the tutorial. A larger, readable version can be viewed here.