Here is an overview of structure charts. If you are still a bit unsure about them, this may help.
The following video explains just one part of structure charts (post test loops) and then extends to show the creation of an algorithm based on the loop and coding based on the algorithm. The example also gives some more detail about how pre and post test loops can be described in a structure chart. Drawing Structure Charts Written Explanation of Structure Diagrams  http://www.drdobbs.com/structure-charts/184402173?pgno=2
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12 SDD > Stem 3.0 Software Development Cycle > 3.1 Defining and understanding the problem > 3.1.4 System Documentation >