Do you just want to include an image/logo that will show up on every
page? If so, what you want to use is the "Slide Master." Go to
[View] --> [Master] --> [Slide Master]. That will bring you to the
page that is essentially the underlying template for each new page you
create. Often, there's also a "Title Master" as well (or an
additional "Slide Master" if you're already on a title slide). If you
want your image to appear on the title slides as well, you'll need to
copy it onto both pages. Just use your page up/page down keys to find
it (or click on it in the "Slide Sorter" view or on the slides on the
left).
Hope that helps!
Kevin