System.Net.Mail Help

Question

Hi every body

i am trying to use mail in my form i have a form name as order form i am taking all the values from the form and i create body of the mail i add from,to,and subject and body to the mail but when i try to send the mail i got some error and i make changes in web.config file also please any one can tell me what are the exact field  i have to use in web.config file i will show you what i write in config file
<system.net>
    <mailSettings>
      <smtp from="">
        <network host="" port="3535" userName="" password="" defaultCredentials="true" />
      </smtp>
    </mailSettings>
  </system.net>

please tell me what i have to write in from=
and in host=
i am very much confused with this please help me its very urgent