Crafting missions are recurring events, typically lasting 10 days. These events have multiple steps, each with approximately 3 tasks. These tasks require crafting items and performing other actions in the game.
Once you've completed all the mission steps, you receive the mission reward.
There are usually multiple missions running at a time. Each mission can be found along the left side of the game window.
Don't forget to read the mission dialog as it provides valuable information!