The DIV is just a tag to represent a division of the page, sometimes called a section of the page, the full details of the tag can be found here:
An AP Div is a DIV tag which you can absolutely position (thus the AP in the name) this means you can place it anywhere on the page.
In Dreamweaver to insert an AP Div you go to the Insert > Div menu item and select it. Once selected it will ask you for a name, in the ID field enter in a name for this div, e.g. logo or menu, etc.
This will create a new “box” (div) in the design view which you can set to be draggable drag around the screen and place where you want. Inside the “box” you can put both images and text.
Additional options are hiding behind the “Show Set” checkbox, please uncheck it.
You should then see the category icons appear under the Properties heading, the categories are Layout, Type, Border, Background and More – by clicking the various icons you will switch modes/views of the CSS that you can modify for each of those categories.