When you set up each email account, OE will have prompted you for the name of the mail servers to send and receive mail.
You must have had this information at some point - for incoming mail it would be something like imap.myisp.com or pop3.myisp.comand and for outbound something like smtp.myisp.com.
On top of this, you may be required to provide a password when you connect to one or both of the above servers.
Again, you should know the username and the password, if you were required to set them up.
It is possible to set these up so that it stores your username and password and connects without you having to enter them every time. Of course it also makes it very easy to forget your password - even username.
All this is configured through the OE properties / settings. I would describe it in more detail, but the PC I'm using at the moment doesn't have OE.