Before configuring Windows Mail, be sure to enable POP/IMAP access and to do other necessary actions in your Gmail e-mail account, see Configuring you Gmail account for using with Windows Mail.
To access your e-mails with Windows Mail using POP, see How to access Gmail with Windows Mail using POP.
To access your e-mails with Windows Mail using IMAP, see How to access Gmail with Windows Mail using IMAP.