You can place them anywhere you want it's up to you to decide where and how you want to access them.
Every user in MacOSX has by default a folder namer Pictures where you can place all your pictures.
Also as you drag them to iPhoto you can arrange them in your iPhoto Library by albums and events.
If you want your images to appear in iPhoto just drag them into iPhoto and they will be copied into your iPhoto library. Other than that there really is no "correct" place for you images.