Welcome to the wonderful world of components. If you're here because you heard about the "Component Rework", and have no idea how to untangle the complicated jargon that is component crafting, read on.
If you're a crafter who's been playing for an extended period of time before December 2018 I suggest starting with the "What's changed?" section. Otherwise move on to "I'm new".
On December 23rd 2018 the entire component creation process was changed, essentially undoing most of the old mechanics.
Stars have been removed from the game entirely, and replaced with a new Item Quality value from 1% to 100%
Tier is no longer automatically generated based on your mastery + input material quality, and is now explicitly chosen by the crafter at time of component creation
Difficulty is no longer complicated and different based on component type\input material. No more 214 difficulty yggdrasweave, folks!
Queues are now used for component creation, meaning no more indefinite running of a single component
Mastery no longer determines top tier stats, and only provides dice
Submastery is now crucially important. It no longer determines the star range of your item as stars have been removed, and that formula was broken anyway. Submastery now determines how quickly your item will be created (much more on this later)
Over Roll now applies to components. While this is not unique to components, it is a new feature that was introduced with this patch and applies to our items as well as refined materials.