He is Found in Firelink Shrine, at the end of the hallway that leads to the back of the shrine, sitting at an anvil.
Andre is a relatively short man, sporting long white hair that is tied back into a long ponytail, and a long white beard. Andre appears to have various scars and burn marks on his upper body and arms, whilst wearing pants, a belt, and gloves. He can always be found sitting at an anvil, forging an Estoc with a hammer. He has a multitude of tools and weapons lying around him. While similar in appearance to Andre of Astora from Lordran, it is unknown for certain whether or not the Andre found in Dark Souls 3 is the same person. Some theorize that they are different people, but Andre's knowledge of the Giant Blacksmith, and references to knowing him for ages, has led some to believe that they are in fact one and the same.
After exhausting his dialogue, he teaches the "Hurrah!" gesture.
Andre will reinforce the player's weapons in exchanged for certain types of titanite, depending on the player's reinforcement level and weapon, as well as souls.
Andre can infuse weapons if the player brings him various coals found throughout the world. Certain coals yield different infusion upgrade paths. Once a weapon is infused, it may still be upgraded by using the type of titanite specific for it. However, the player should take into consideration if infusing a weapon affects it negatively, according to their stats, or if doing so will remove its scaling bonuses.
In addition to upgrading and infusing weapons, Andre can repair those that are broken. He cannot repair the Ring of Sacrifice, though.
Andre allows the player character to allocate between a standard Estus Flask and the Ashen Estus Flask. For example, if the player has five Estus Flask uses in total, they can choose to have three standard Estus Flasks uses, which recover HP, and two Ashen Estus Flask uses, which recover FP.
Finally, Andre can reinforce the player's Estus Flask to increase its number of uses. In order for Andre to upgrade the Estus Flask, the player must bring him an Estus Shard.
If the player kills Andre, he will no longer offer any services, unless the player's sins are forgiven at the shrine of Velka.
Click to see dialogue
"Well, a newcomer I see. I am Andre, I serve in this shrine as a humble smith forging new weapons. You're in search of the Lords of Cinder, I trust? A toilsome journey, I wager. You'll require good arms. Let me smith y' weapons. I am a smith, such is my purpose."
"Ahh, well met. Tis good to see y' in good health. What needs smithing this day?"
"Prithee, be careful. I don't want to see m' work squandered!"
"Weapons and protection are sturdy enough, by and large. But when overused, they'll eventually break. When their durability is low, repair becomes a necessity. Use a powder, or simply rest at a bonfire. But should chance impel them break, bring them to me. I'll hammer 'em back into shape. They take no pleasure in breaking, I assure y'. So handle them with care, if y' would."
"There are two ways to smith weapons. Simple reinforcement is one, and infusion the other. Reinforcement is straightforward. It strengthens a weapon without altering its property. Infusion is a more advanced form of smithing that infuses an element. Reinforcement requires titanite, and infusion requires gems. Bring the stones and I'll do the smithing. It's m' purpose, afterall! In battle, y' weapons are yer only friends. Forge them well, and they won't let y' down."
"Oh, by the by. If you find any Estus Shards, bring 'em 'ere. They can be used to reinforce either of y' Estus Flasks. Without those flasks, you'd want for life or focus. And they'll always stay with y', why not treat 'em well?"
"Ahh, another matter. Infusing weapons with gems requires a special kind of coal. My humble coals won't be any use infusing more unusual gems. I know, it's an awful shame, but it's all I have. Oh, please, don't give me that look. Believe it or not, I'm quite thin-skinned."
Giving him the Farron Coal
"Oh, my... this coal is from the Undead Legion... Used to forge the weapons of Farron's Abyss Watchers. A fine prize. I'm honoured to be endured with it. Now I'll be equipped to infuse special gems. Praise the gods, eh. Time to put this brawn to use!"
Giving him the Sage's Coal
"Well, well... What's the Undead Legion doing with a coal such as this? I'd heard one of the Crystal Sages had sided with Farron's Abyss Watchers. I suppose it must be true. You should know, this coal is imbued with magic. First one I've ever seen. Hardly a surprise is it? I've never been one for books or wise men."
Giving him the Profaned Coal
"Lords... Where didye hap'n upon this coal? This is much too dark. I see the Abyss in it... Yet, a smith I remain. I won't turn down a request. But forget not, Your fight is for the flame, and for y' fellow kin. Just like mine. A cursed fate this may be, but hope remains, does it not?"
Giving him the Giant's Coal
"My, my. the coal of that peaceful giant... Seems like ages past... I imagine his passing was long ago. I miss the old bugger, I do. My thanks. I'll be sure this coal is put to good use. I'll be smithing weapons never afore seen by the likes of y'. It's but a small service, to pay my humble respects"
Twinkling Dragon Torso Stone, once Hawkwood leaves Firelink Shrine
"Oh, you've returned. I was hoping to see y'. That crestfallen arse Hawkwood, he handed me this. He's changed a great deal since he left this place. Graven of face, he asked me to give it y'. Well, now that that task is concluded... What would y' ha' me smith today?"
When attacking him
"Enough of that!"
"Beshrew your heart..."
Talking to him after killing him
"Overstep not your bounds, cousin. I may serve, but I'm no slave. I have business I must attend, begone."
↑http://soulslore.wikidot.com/das3-interviews (March 2016 Famitsu interview with Miyazaki): the interviewer asks "Is the appearance of Andre, the blacksmith, a result from finishing a chapter of the history?" To which Miyazaki responds: "Um. Rather, Andre is there for a minor amusement. Actually, since the first Dark Souls, we were developing him as a part of 'the Clan of Andre, the blacksmith'. And we thought all those Andre looking corpses with embers were exact look-a-likes, and this time, it is the same idea."
(Continuing response from above, Miyazaki states): However, the world in DS3 is an accumulated continuation of DS1 and DS2 that characters from previous two games returned in different forms or with added background story. It sounds weird but like, "DS3's the next in the series, so there is a way to have them back like this."