Patricia,
You simply cannot do this. All you can do is draw a textbox yourself, but
this will of course appear on each of your slides and you will not be able
to edit the contents.
Luc
You cannot create new placeholders. You are limited to a 'title' and a
'bullet list' placeholder only.
You can insert a "title master" to create another slide master....but you
are still limited to two placeholders.
If you need extra text on each slide...e.g. a sub-title. Then it's probably
easier to create several slides. Then duplicate the slide before editing it.