An empty grave counts -3 graveyard quality. Once a body is buried and the grave gets a headstone and a fence, it counts the headstone plus the fence minus the body's red skulls, never more than the body's white skulls. Each new best graveyard quality also counts towards the Resting Place inspiration. It is on the blueprint desk from the start, with no technology needed.
Graves go on the grave plots of the Graveyard's areas: 6 in each Grave Area I and Grave Area II, 4 in each Grave Area III, Grave Area IV, Mixed Area I, Mixed Area II and Mixed Area III. Each area kind can be built twice, and the Graveyard starts with one more Grave Area I, so it holds at most 70 graves.