Not sure Ethel explained it very well (sorry Ethel).
Your e-mail first arrives at your ISPs server.
When you look at your e-mails it downloads them from the server to your PC or laptop.
Once downloaded from the server they are not downloaded again, so they go to EITHER your laptop or your PC, whichever one you used first to look at your mail.
It is possible to set Outlook Express to LEAVE e-mails on the server, so they would download to BOTH your laptop and your PC.
If you want to know how to do that let me know (I did explain it a week or so back on another answer)