I need a video or slideshow. I can't figure it out.

There is a note book in your inventory, use it to open the menu with the load/save options.

Here a screenshot, the pointer is on the said note book.

I know about the notebook, but I don't know how to save with it. I've put a few notes in it, but that doesn't do anything.

Open the notebook:
Make Entry ==> Save
Read Entry ==> Load

If you can't load nor save, try running the game as administrator (right-click the game's start icon and select "Run as administrator"), because maybe you don't have write access to the save game location.

I've been making entries and reading them, but nothing happens. I'll see if running it as an administrator does anything.

Does anyone know where the savefiles are stored?
Patricularly in the Mac version?

In linux they are in /home/<user>/.scummvm