Do you have thousands of photos you've taken with a digital
camera spread all over your hard drive? Now might be a good time
to begin organizing those photos and this seemingly overwhelming
task can be made easier with Apple's iPhoto. In this tutorial,
I'll show you how to add several libraries of photos to
iPhoto.
Before starting, transfer the photos you want to organize to your
Mac but not into iPhoto. You might want to place them into
general folders, such as family or trip. This will make it easier
to locate the files for importing into iPhoto.
1. Press the Option key while launching iPhoto. Instead of opening, iPhoto will give you the option to create a new library or open an existing one.

Click the Create Library... button. Name your new library in the pane that opens and select a location on your hard drive for storing the library. Click the Save button.
2. Select Add to Library... from the File menu in iPhoto (Import to Library... in iPhoto '08). Locate the folder of photos you want to add to this library.
3. Once you've imported your photos, it's time to start organizing them. In versions of iPhoto prior to iPhoto '08, open the iPhoto Preferences Pane and select the Keywords tab. You'll notice that Apple has provided some keywords that you can use, rename or remove. To add your own keywords, click the Add button in the lower right corner of the pane and type your new keyword. Create as many keywords as you want. In iPhoto '08, you can create keywords with step 4.

4. Select Photos (iPhoto '08) or Library (versions prior to iPhoto '08) in the left pane of the iPhoto window. Next, select all photos that fit one of your keywords. To assign that keyword to all the selected photos at one time, in versions prior to iPhoto '08, press Command-I and select the Keywords tab on the pane that opens. Put a check in the boxes in front of all keywords you want to apply to the selected photos.

In iPhoto '08, select Show Keywords from the Window menu. Click a keyword on the pane that opens to add it to the selected images. Click the Edit Keywords button to add new keywords.

Continue to add keywords to your photos until all of your photos are labeled.
5. You can now easily create albums that contain just
the photos you want. Select New Smart Album... from the
File menu. In the pane that opens, set criteria for your album
according to keywords. For example:
Keyword is Beach
Keyword is Seagulls

Every time you add the keywords to additional photos, the new photos will automatically be added to your Smart albums. You can create as many Smart albums as you want and combine criteria to create the exact set of photos you want. For example, if you are lucky enough to have many grandchildren, you could use keywords to create a Smart album of photos of all your grandchildren when they were a certain age. The options for Smart albums is limited only by your imagination.