Click on the Text tool (the capital T). In the tool options pick a font, size and color and then click where you want the text and start typing.
In case you are looking to have a text on the exact boundary or any specific area then you have Text on Path tools to help you. Just select any of the text on path tools from text tool category. Here is the help link to help you heer http://help.adobe.com/en_US/photoshopelements/using/WS287f927bd30d4b1f-deece6d12e28b17def- 7fff.html
For your case using Text on selection would work perfectly.
Hope it helps.