Another newbie question with PPT 2010.

I am struggling to understand the relationship between Slide Masters, slides, and templates. I am writing a VB app that will automate creation of a presentation containing many (indeterminate number) of slides. Since we may want to have different themes for the same content, I intend to implement this with a template containing perhaps several Slide Masters.

I understand (I think!) how to use a template and the purpose of Slide Masters and slide layouts. I have created a Slide Master with the first theme, which has a few placeholders -- a couple of text boxes and a picture placeholder. However, when I created a presentation based on this template, I can't edit the shapes' content on the first slide in the presentation, which is based on the Slide Master - they seem "locked". If I select the Slide Master itself I can edit the shapes' content. I thought that the Slide Master is kind of a template itself for the slides that are based on it, so I would have expected the reverse behavior - locked Slide Master and editable slides.

If I add shapes to the slide directly I can edit those shapes, but not the ones inherited from the Slide Master.

I have searched the MS site for useful tutorials and re-read the Help tidbits many times, but have to admit I am still confused by these relationships. Any help or suggested links is greatly appreciated!