Setting up Mail.app to use with common free webmail accounts is very simple in Leopard. Mail.app does all of the heavy lifting for you. I'm pretty sure this feature is not available in Tiger.
Simply launch Mail.app from the Dock (It is the icon with the stamp with the eagle on it). If it is the first time you are setting up an account in Mail.app, you are taken directly to account set up. If you have at least one account already set up, you will need to go to Maill.app Preferences and click on the Accounts tab. Click the + button on the bottom right of the preference panel.
At the Add Account panel:
- Enter your name, email address and password (this is the password you use to log into your email on the web.)
- Hit the Create button.
You can have multiple email accounts active at once in Mail.app, and Mail.app will check them all at once. I have my iCloud email account and several different Gmail addresses that I use for different projects. Rather than log in and out of Gmail's web client every time I want to check mail, I have them all set up in Mail.app.