For the default ISP address you set up you go through the OE setup wizard and use the user name and password provided by the ISP you use. There you create an alias address. For example for emcx2 for a user name and xxxxxx for a password you would use the imaginary firstname.lastname@example.org
for the new account in OE.
For bringing in mail from an exsting online account like Gmail, Inbox.com, fastmail, or others disregarding MS hotmail you would have to manually configure the POP or IMAP type server and enter the address to see that done.