Have you written any software before?
Do you have experience with writing flowcharts for anything? Or using other programming languages?
I would tend to suggest structure diagrams, because flowcharts don't lend themselves intuitively to well designed software.
If you're going to use flowcharts, start with something very simple, then do flowcharts for each of the blocks that you define, keeping these simple as well. Keep going until you have the problem defined to a level you feel you can code.
Potentially, each of those flowcharts at the lowest level will become a subroutine (especially if you find that you've referred to them in multiple places) with the upper level flowcharts being your main routine which calls these subroutines as required.
It is possible to write one huge flowchart in full detail, but you will need a huge piece of paper, identifying subroutines will be harder, and coding it will possibly create a mess.
I'm not sure how much this helps...