Well the installer must have asked you to input a password during installation.
Well if you dont remember you will have to boot into runlevel 1 and change the password.
1. When you first start your computer, the GRUB screen (where you choose your Operating System) appears. Select the Fedora that you want to boot into, but press the "a" key instead of pressing Enter.
2. You will see a line somewhat like the following:
kernel /vmlinuz-2.6.9-1.667 ro root=LABEL=/ acpi=on rhgb quiet
kernel /vmlinuz-2.6.9-1.667 ro root=LABEL=/ acpi=on rhgb quiet 1
You will then boot into single user.
Type in passwd at the prompt and you should be able to change your password.