Mail puts all the email you get into your Inbox; the statistic after the word Inbox lets you know how many messages you haven't yet read. New messages are also marked with light blue dots in the main list.
The Mail icon in the Dock also shows you how many new messages you have waiting—it's the number in the red circle.
Click the Inbox folder to see a list of received messages. If it's a long list, press Control-Page Up and Control-Page Down to scroll. Click the name of a message once to read it in the Preview pane, or double-click a message to open it into a separate window. (If a message is already selected, pressing Return or Enter also opens its separate window.)
Instead of reading your mail, you might prefer to have Mac OS X read it to you, as you sit back in your chair and sip a strawberry daiquiri. Highlight the text you want to hear (or choose Edit→Select All), and then choose Edit→Speech→Start Speaking. You'll hear the message read aloud, in the voice you've selected on the Speech pane of System Preferences (Chapter 9).
To stop the insanity, choose Edit→Speech→Stop Speaking.