If you're logged in as root at the command line, you won't need to enter either a username or a password under e-smith 4.1x, as the password is stored in /root/.my.cnf. If you need the password for other reasons, again, look at that file.
As to "what to query", that's going to depend very much on what you want to do, but probably checking the MySQL docs at
www.mysql.com would be a good idea.