Suse's installation program must have asked you to enter root user's password..... Enter that password when the login screen asks you for a password.... After root user's desktop comes up, then using the control panel , add more users to your system that you can use for normal use....
Enter # kuser to start KDE User management program.
If you forgot root's password also, then when GRUB comes up during system startup, append single to the boot string. that should start linux in single user mode without asking for any password.... now you can change root password by giving # passwd ... then start your system again and login as root as explained above...
You might also want to use # adduser command....