i just only finish install Red Hat linux
... which one?
i also want to try how to install BOOTLOADER(LILO&GRUB) manually, so i skip install boot loader during installation.
... and you did this without first finding out how to do this and not realizing that a bootloader is needed in order to boot? <sigh>
In the first place, it is inadvisable to install more than one bootloader at a time.
You need to boot from your install media and enter "linux recovery" at the boot: prompt. This will get you a root shell prompt (#) in single-user mode.
IIRC: you then need to enter "grub-install /dev/hda"
There are more complex approaches:
This will get you a bootable system. The rest of your questions are copiously answered on the web and in these forums. Happy hunting.