Create a text box and place it in the Report Footer of your report. You might have to select the option to turn it on from the menu bar... click View and select the Report Header/Footer option. Key this into the Control Source of your text box...
="Number of records = " & Count([YourFieldNameHere])
The "YourFieldNameHere" value must be the name of one of the fields in your record souce that you want counted.
HTH