In a nutshell, crafting involves hiring numerous NPC assets to complete crafting-related tasks. These NPCs include Leadership Mercs, Platesmithing Miners, Mailsmithing Prospectors, Leatherworking Skinners, and Tailoring Weavers. Over time, completing various tasks will award profession XP as well as resources and rewards.
Your NPC assets will work on your tasks while you're out adventuring, and you can also "tinker with your professions on the Neverwinter Gateway website when you're outside of the game client," according to the diary. Learn more at the game's official site.