Crystal Reports report building

We need a few reports designed. The reports are simple. The problem we are hung up on is prompting a new sub report to generate based on variables in the main report. This is not for viewing in crystal reports viewer. The reports are used in our POS software and can not be changed at time of printing. They only look at static data. We can design and change the reports to our liking we are basicly just needing help with the generation of an additional report to print at time of main report if a condition is met in the main report.