After you have executed make modules_install
from the Linux source directory - most likely /usr/src/linux - and copied the kernel image file to /boot, open up the grub config file in your favourite text editor. The config file is usually /boot/grub/menu.lst or /boot/grub/grub.conf. A simple entry for a kernel image could look like this:
title My own 2.6.7 kernel
kernel (hd0,0)/2.6.7-myown root=/dev/hda1
That's the simplest kind of entry. Some people (and distributions) prefer using initrd kernels, in that case you'll need another line in the grub entry.
Also refer to your distribution's documentation, it could provide valuable information on how things are expected to work on your distribution.