Enchanting: Start-up Costs - Novigrad (Hearts of Stone)
Location: Upper Mill
Quest Giver: Notice Boards in Velen
Other Requirements: Hearts of Stone DLC
This quest is given to you shortly after arriving in Velen for the first time if you have the Hearts of Stone expansion enabled on your install of Witcher 3. You most likely won't be able to complete it until much later though since it is a higher level quest.
However, for this quest all you really have to do is give the NPC 5000 Crowns to begin work on his craft again. The next quest will have you fight enemies in their 30s though and be much harder for you at a lower level. If you're unfamiliar with the Runecrafter profession I highly recommend you google it and read into it - it's extremely useful.
Basically the long and short of it is the Runecrafter Profession can be used to both add sockets to your armor as well as enchant your sword. There are many unique upgrades to Runecrafting that you can get to boost your character's strength and potential. I go into more detail about the enchants I use and why on the next page
Completing this quest leads to the follow up, Enchanting: Quality Has Its Price.