The flow chart shows your processes and decisions that must be made when creating your product. Below is a flow chart that was created in Google Drawings. I recommend you do the same.
Here you can see the most important symbols for a flow chart. I recommend that your chart consist mainly of "processes" and "decisions." In other words, you should have a lot of rectangles and diamonds (and arrows, obviously) on your flow chart.
Here is a link to my sample Gantt Chart.