Applications :: How To Add Images In IPhoto

I'm having trouble adding images in iPhoto. I want to create a book. An "event" was created when I downloaded the images from the camera but there are other images I want to add. When I drag and drop the images I want to add to the event ( from a folder on my desktop where I put them) it creates a new event, it does not add the images to the event I want them in. So I created a event with the new images I want to add and merged the two events but the new photos do not show in the bar across the top where the images are for me to add to the book.

What am I doing wrong, how do I add images to a event?