I am sorry but I couldn't quite understand what you were trying to do. A link to that tutorial that you watched would help a lot.
But here are some very short instructions:
(1) If you want to use a mask made of white and black, remember just this point: BLACK HIDES AND WHITE REVEALS.
Save such a file as JPEG
and not as a png.
Producer will use this file as a mask and mark it automatically as GRAYSCALE.
(2) If you want to use a png file, use white as the color to reveal, and use transparency instead of the color black. Producer will interpret the transparency as black, and only the white part will be revealed.
This kind of file will be automatically categorized as a TRANSPARENCY mask.
(3) I'm guessing that you are talking about using text as a mask.
Producer 7 (and 6) are capable of creating TEXT LAYERS. You don't have to prepare anything in Photoshop.
Just create your caption, using the color white, and then convert this caption to layer (Right click > Convert to Text Layer)
When this text layer is used as a mask on top of another layer with a picture, the picture will be visible only through the letters of the text. Producer will categorize this mask as "Transparency".
AS A RULE:
You can only see the results of what you are doing, while working on the slide, ONLY if you select the layer UNDER the mask and not the mask itself.
Hope this helps a bit. I wrote it as simply as I could.