Once the base system is installed you are asked to reboot the system. Remove the floppy disk and CD-ROM and reboot the machine. Keep the floppy in if this is how you plan to boot into Linux (otherwise you are probably using LILO to book directly into Linux).
You will be asked to enter a password for the root account and to create a user account. Do so. In general it is best to log in as a user then use the su command to set the user to be root as needed (e.g., to install packages or modify files in /etc).