How do people come up with all these intricate designs with lots of detail? How do you turn an idea into 3d? Is it based on concept art first or can you just make your idea in 3d first? What are some resources for learning this stuff?
Imagination!
Once you learn the basics of 3D you can make anything you can imagine.
Check out the Mesh Modeling Bootcamp to learn the basics and set you on the road to creating what ever you wish.
When learning to model the coffee cup for example try to think of what you are doing with the tools not just the end result.
A surgeon needs to know what the tools on the tray are for and how they work before making the first incision.