Let's take an in-depth look at each part of the Arduino Uno's PCB to get a better understanding of how the Arduino works at the hardware level.
Intro to Arduino : 15 Steps (with Pictures) - Instructables
Arduino Nano — Arduino Official Store
What is Arduino Uno Hardware Board? Everything you need to know about the Arduino Hardware
An In-Depth Look at the Arduino Uno PCB - Circuit Basics
How to make an Arduino UNO at Home? DIY Arduino Board
Arduino Prototype to Manufacturable PCB: An LED Multiplexer
Arduino Board Components Explanation
Arduino - Circuit Basics
DIY Arduino UNO How to Make Your Own Arduino Uno Board : 8 Steps - Instructables
Fun with Arduino 02 Digital Input and Output – Fun with Arduino