In the Field Explorer, right-click on Formula Fields and select New. Give the formula a name and enter the formula that Sarah mentioned. Save it. Then you can drag and drop it anywhere on your report. Another alternative is to right-click on the field you want to summarize and select Insert > Summary and then pick Count as the summary calculation.
If you're new to Crystal Reports, you might want to check out my Crystal Reports Encyclopedia book with many tutorials to get you the right start. You can find out more about my books at
Amazon.com or reading the
Crystal Reports eBooks online.