To add email accounts, just go to Tools, Accounts, Mail tab, and click on Add. On the General tab of the Properties panel for an email account, you can check or uncheck the box for "Include this account when receiving mail or synchronizing". If you leave it unchecked for a certain account, you can always manually make OE retrieve mail for that account.
If you have multiple users of a computer and want to keep email separate for each person, you can do that by creating a separate Identity for the other user(s). Alternatively, you could use one Identity and then use Message Rules to direct all mail to one recipient into one or more OE folders.
