Sitting in Firelink Shrine, he can upgrade your weapons as well as improve and adjust your Estus and Ash Estus Flasks. Bring him upgrade materials to improve your weapons and shields. Special, named Coals give him the ability to Infuse equipment in additional ways; he’ll be able to make them scale to different attributes, or to gain special aspects.
Andre returns to the shrine if you kill him, but he won’t craft anything for you, or serve any of his other functions. To get his loyalty back, go to the Undead Settlement. Near the Dilapidated Bridge Bonfire is a sewer area. Down there you find an altar to Velka. Bring plenty of Souls, pay for your sins, and be absolved.
Andre is likely the same Andre of Astora from long ago.