You can have a look at the Grub package (.rpm if you're using RedHat) which should contain the basic grub configuration file (that's what you're looking for if you haven't done any changes yourself). However for a quick start you can write it yourself like described above.
Note that you'll need to check that the "root", "kernel" and "initrd" lines match your configuration.
"root": the partition where your kernel and other boot-related files are; first number means disk and second partition, starting from zero. Fist partition of primary disk is "(hd0,0)", second partition of primary disk is "(hd0,1)", first partition of secondary disk is "(hd1,0)" and so on. This is either your root partition, or if you have a separate boot partition, then that.
"kernel": path to the kernel file, assuming that root ("/") is on the partition mentioned in the previous line. If you have a separate /boot partition and the files are there, the paths are like in watcher69b's post. However if your /boot is on your root partition (= you don't have a separate boot partition), you probably need to add the "/boot" to the path, so following the above post example the line would become
kernel /boot/vmlinuz-126.96.36.199-29.fc9.i686 ro root=/dev/VolGroup00/LogVol00 rhgb quiet
This is because now the files are in a directory called "boot" which is in the partition's root; in case of a separate boot partition the files probably reside in the boot partition's root directory. The option "root=" tells, like it says, the root partition, and is like above ("/dev/VolGroup00/LogVol00") if you are using LVM, but if you are not (your partitions are just normal partitions) it's probably "/dev/sda1" (first partition of primary disk) depending on the partition. If this is wrong, Grub fails to boot
With some kernels you'll need to use "hda" instead of "sda" in this case if you have an IDE disk..
"initrd": basically same story as with "kernel" line: path and filename of "initrd", relative to the partition mentioned in the "root" line.
The other lines are optional as far as I know, but at minimum you need the lines starting with "title", "root", "kernel" and very probably "initrd".