This increases the amount of souls you gain for a limited time, but you have to be embered for this to take effect. After you ember yourself, use a dried finger. To get more HP and survive longer, ember yourself while doing this. This can be done with any bonfire to respawn enemies. You can kill them again with minimal difficulty and work your way back to Firelink Shrine.
Then, teleport back to the first area and all the enemies will have respawned. Thus, once you reach the Firelink Shrine, use the bonfire.
