This page of the Elden Ring game guide contains information on where you can meet an NPC called White Mask Varre. You will also learn how to complete his quest chain and what rewards await you for completing it.
White Mask Varre will appear at the very beginning of the game. You will find it after leaving the tomb (tutorial) in Limgrave, more precisely by the Site of Grace, called The First Step.
How to proceed with the quest?
Most of the time, Varre will be in Limgrave, by the The First Step Site of Grace. His questline will move forward only after you defeat Godrick the Grafted boss. After you defeat him, go back to the The First Step Site of Grace Talk to him and then agree with him.
Then, Varre will appear in a different location. You will have to move to the Rose Church located in Liurnia of the Lakes.
Once you are there, Varre will be waiting in front of the church entrance. Talk to him and exhaust all the dialogue options.
He will give you 3 Festering Bloody Fingers. They are used to invade other players' worlds. Your task will be to use them three times. The result of the raid is irrelevant - you can win or lose, and even if you leave the world of another player, you will complete the quest.
Then, Varre will ask you if you want to join the Bloody Lord. If you answer yes, you will move forward with the task. You will receive a key item, the Lord's of Blood's Favor.
Then you have to get to The Four Belfries Site of Grace in the northern part of Liurnia of the Lakes. At the top, you will find a chest with Imbued Sword Key, which will allow you to unlock one of the three teleports located by the belfries.
Go to the second belfry and insert the key into the gargoyle. Then, interact with the teleport. You will be teleported to the starting location from the tutorial.
If you haven't defeated the Grafted Scion boss the first time, you'll have the opportunity to fight him again. After defeating him, go to the very top and enter the building.
There will be a corpse inside the building. Interact with it so that the item received from Varry will be stained with blood. Then go back to the Rose Church and talk to Varry.
During the conversation agree to his offer. This will give you a new key item, the Pureblood Knight's Medal. With this item, you will be able to move to one of the end locations, Mohgwyn Palace.
It is worth noting that this is a difficult location to go through. Both the regular opponents and the boss, Mohg, Lord of Blood, should be fought only by a well-equipped and upgraded character.
When you get to the Mohgwyn Palace, go up the stairs. Watch out for many zombie-like enemies. Some of them explode, and the cloud of the blast inflicts a bleeding status. Go upstairs and then into the cave. After killing a few enemies, you should see Varry's sign at the very end of the cave.
However, before you interact with the sign, leave the cave and use the Site of Grace - only then visit the Varry's world. Watch out for his attacks, as they cause a lot of bleeding. You can summon Ashes for this fight to make the game easier.
Rewards for completing the quest
After you get out of his world, go to his corpse. After his speech, you will receive Varre's Bouquet and 6 Festering Bloody Fingers. The medal, which will transport you to Mohgwyn's Palace, can also be considered a reward, as the location is perfect for acquiring a large number of Runes.