This mod does exactly what it says it does.
When you die, a grave will spawn.
Upon respawning, you will be given a compass that points to your grave.
Graves last for 86400 ticks, or 72 minutes. This timer only counts down when your grave is in a loaded chunk. You may only have a maximum of 10 unclaimed graves at any time. If you exceed that maximum, your unclaimed graves will be deleted, starting from the oldest grave.
They store half of your experience points, not levels, and you regain the experience when you claim your grave.
You can read more about this mod on their Curseforge page.
