Hi Marcelo
In the PageHeader section of your report you can add a label that can be configured to show the count of work orders. Have a look at this video tutorial then follow these quick steps and you should be able to hit the ground running.
Step 1 - Drag a label into the report's PageHeader section
Step 2 - From the Data Binding dropdown select which field you wish to count. I chose Activity.ActivityStatus as that was one of the fields on my report.
Step 3 - Click the ellipses button next to Summary. Set the Summary Function to 'Count', click the Format String ellipses button, ensure it is on the General Category and enter a Prefix such as 'Total Work Orders: ' and click OK.
Step 4 - Select the Report option for Summary Running, click OK then preview the report. With a bit of luck you should see the new Total Work Orders count
Let me know if you can't get it to work or if you have any further questions.
Jef