This battle takes place in the Tomb of the Giants which is accessible through the Catacombs after defeating Pinwheel.
Gravelord Nito is one of four primary bosses that you must defeat to open the path to the Kiln of the First Flame which leads to Gwyn, the game's final boss. The Tomb of the Giants is one of the more challenging areas of the game because there is very little natural light, forcing the player to create their own light source, and the enemies are aggressive and hit hard.
There are three ways to create light:
1) Skull Lantern, which can be equipped and held like a shield. They can be dropped by catacombs necromancers and one can be found on a corpse in the pit Patches kicks you into in the Tomb of the Giants.
2) Cast Light sorcery, which is sold by Dusk of Oolacile and requires 14 INT to use.
3) Sunlight Maggot helm (my preferred option), which is always dropped by a Sunlight Maggot in the Lost Izalith shortcut (which can be accessed by going through Lost Izalith the proper way if need be).
As you progress through the Tomb of the Giants, you will eventually reach an outside-ish area that is fully lit with a cliffside path that leads to a cave. Head into the cave and continue past some enemies into an open area with Pinwheel Servants where you will find find the fog wall to Nito behind some easily breakable bones and debris. You can traverse the light without starting the encounter- you must drop off the ledge into the room below before the Nito battle begins.
The Nito area is somewhat large but you want to try to stay close to where you fall in as to not aggro numerous skeletal enemies. Three skeletons will always engage you and unless they are killed with a Divine weapon, then will come back to life for the duration of the battle. Your best option here is to find the Occult Club in Anor Londo and have Andre modify it down to Divine +5, use it to kill the three skeletons, and then switch to your primary weapon for Nito, who will make his way towards you as you are dealing with his minions.
Other weapons that have innate Divine property are Astora's Straight Sword, Crescent Axe, Silver Knight Spear, and Grant. Most have a Faith requirement, though.
Nito will use a combination of magic and melee attacks, most annoyingly the Gravelord Sword Dance miracle that makes red spikes burst from the ground that are difficult to avoid. He moves and attacks fairly slowly, so the battle shouldn't be too difficult as long as his skeletons aren't a constant harassment.
Once you defeat Nito, the achievement will unlock. Good luck!
As always, refer to for specific information relating to items or locations.
