You can create a new ideabook at the same time you add photos to that ideabook. The instructions are pretty straight forward. When you find a photo you'd like to add to a new ideabook, click the "add to ideabook" button below it. Then, choose "or new ideabook" and type in the name of your new ideabook in the blank space to the right. click on the "add to ideabook" button at the bottom and the photo will now be in your newly created ideabook.

When using the ipad, after clicking "add to ideabook", I do not see "or new ideabook".

In the iPad, after you tap add to ideabook, there is a select ideabook button with the name of the currently selected ideabook. Tapping that button lets you select another or create a new one.