I lost the original downloaded calendar app that came on the phone - how do I get it back? i believe it was the gmail calendar since it synced automatically with the one on my computer.
Are you saying that when you go to the applications drawer (circle with triangle in it at the bottom of a screen) there is no calendar app listed among your applications? Or did you just lose the widget that appeared on one of the screens? If it was just the widget then a long press in an open space on a screen > Motorola Widgets > Calendar. Afterwards set it up as you wish. Be sure you have plenty of open space on a screen since it may take up 2 or more single widget/shortcut spaces.
If you lost the calendar app from the app drawer it may take a reboot/battery pull or worse case a factory reset to get it back.