Trouble shooting
What if the spelling doesn’t seem to work? 
This likely means that spelling was not turned on.  To turn spelling on go to Edit and select Spelling.  At this dialog select Beep on questionable spellings ... and click OK.

   
What if the LEARN button is grayed out? 
This means you have to select the User Dictionary.  To do this choose Select Dictionaries... from the Edit menu above.  Then Select the User Medical Dictionary, which should be in the Claris folder in your System folder!  Make sure the Select Dictionary Type says User Dictionary