First enable POP in your mail account from web interface:
Log in to your mail account.
Click Settings at the top of any mail page.
Click
Forwarding and POP
in the orange Mail
Settings box. 
Select Enable POP for all mail or Enable POP for mail that arrives from now on.
Choose the action you'd like your messages to take after they are accessed with POP.
Configure your POP client* and click Save Changes.
-------------------------------------------------------------------------------------------------------
Open Outlook or Outlook Express.
Click
the 'Tools' menu, and select 'Accounts...' 
Click
'Add,' and then click 'Mail...' 
Enter
your name in the 'Display name:' field, and click 'Next.' 
Enter your full email address (ex.: 'chris@mydomain.com') in the 'Email address:' field, and click 'Next.'
Enter 'pop.gmail.com' in the 'Incoming mail (POP3, IMAP or HTTP) server:' field. Enter 'smtp.gmail.com' in the 'Outgoing mail (SMTP) server:' field.
Click 'Next.'
Enter your full email address (ex.: 'chris@mydomain.com') in the 'Account name:' field. Enter your password in the 'Password:' field, and click 'Next.'
Click 'Finish.'
Highlight 'pop.gmail.com' under 'Account,' and click 'Properties.'
Click the 'Advanced' tab.
Check the box next to 'This server requires a secure connection (SSL)' under 'Outgoing Mail (SMTP).'
Enter '465' in the 'Outgoing mail (SMTP):' field.
Check the box next to 'This server
requires a secure connection (SSL)' under 'Incoming mail (POP3).'
The port will change to 995.
*The order of 'Outgoing' and
'Incoming' mail server fields varies by version. Make sure you enter
the correct information in each field. 
Click the 'Servers' tab, and check the box next to 'My server requires authentication.'
Click 'OK.'
Congratulations! You're done configuring your client to send and retrieve messages.