You navigate the iTunes Store aisles just like a Web browser. Most song and artist names are hyperlinked—that is, click their names, or album cover images, to see what tracks are included.
Click the upper-left corner's Back button to return to the page you were just on, or click the button with the small house on it (circled below) to jump to the Store's home page.
When you find a performer you're interested in, click the name to see a list of available songs or albums. If you click an album name, all the songs available from it appear below, in the Details window. Double-click a track title to hear a 30-second snippet. Short previews of items in the Store's audio book and video collection are also available, as are movie trailers.
When browsing the store, you may see a small, gray, circular icon bearing a white arrow in some columns of the Details window. That's the "More Info This Way!" button. (You also get the Little Gray Arrows on tracks in your own library because iTunes wastes no opportunity to get you to visit the Store.) Click the arrow to jump to a page bearing details about the subject, like a discography page, or the main page of artists for the genre listed.