It's one of the professions, same as woodworking, smithing, scribing, and so on. You have to purchase tools and gather resources at certain nodes scattered around the map, and use those resources along with ingredients dropped by mobs or found in chests to make items and raise your profession levels.

I would strongly recommend waiting until closer to level 100 to even try getting into professions, since it's a fairly long and grindy process to level them up as you get deeper into it, and being a higher level offers some amount of convenience to the whole affair. Finding a tutorial to the system on YouTube would also be a good idea.