To log in on a terminal use the username and password of the account that you created during the installation of Kubuntu. In the case of a DVD installation it is by default linuxmce/linuxmce.
To log into the web admin you can to use the name of any user created with the stup wizard, the password has been set to the username as well unless you have already changed it.
When you run the Setup Wizard and create you first user that user becomes the 'Master user' and has the ability to change any setup or setting accessible from the Web Admin site on your Core. If you add additional users when in the Setup Wizard then they are by default not able to change settings in the Admin Web site. If you login to Web Admin as your 'Master user' then you can go to Wizard -> Basic Info -> Users and tick the box "Master User (can modify configuration)?" next to any users you have already created and then click 'Save' to make them 'Master Users' too.