Understanding the components of the arduino uno microcontroller

Is there a place online where i can learn everywhere about the arduino hardware and how it works in depth that covers everything so lets say if i was to make my own micro-controller board I would understand how to do so.

This same website, go to uno product section.

This same website, go to uno product section.

Ok I went over it and it changes my question. Is there a place where i can learn about the actual Atmega (since its the main bit of the arduino) and what does it do and how it works

The atmega328p datasheet would be the place imo.

My book also goes into some depth on the microcontroller to explain things in friendlier terms.
Available at Amazon and other book retailers.