This section lets you configure one or more different mail server setups. You can have many difference mail servers installed. Gmail only uses one at a time, the one that is marked 'default'.
Double click on a mailsetup in the list to edit its values.
You POP3 username, password and server should all be given to you from your Internet Service Provider. Your SMTP server is the server used for outgoing mail. If you are not sure what it is, put your POP3 server there as well.