Single-click the iPhoto icon in the Dock, or go to the Applications folder (click the Applications icon in the Sidebar of any open Finder window), then double-click the iPhoto icon. The iPhoto window (below) opens, although yours will be empty if this is the first time you're using it.
The Library (top item in the "Source" pane below) stores all the photos you import. You can create separate Albums (pages 1819) to organize selections from the Library into easy-to-use collections.