The 16u2 pinout is the same for Arduino Uno/Mega. Keep in mind that the Leds have inverted logic. Writing LOW means turn them on. 16u2 Pinout [NC] = Not connected on an Arduino Uno/Mega R3 D0 - [NC] ...

The webpage by Arduino (ArduinoToBreadboard) explains a way to go from an Arduino UNO to an Arduino clone on a breadboard. Very exciting, ... Step 3: This requires to gain some knowledge about ICSP ...

Both the Arduino Nano and Uno can be powered via their integrated USB connectors. This automatically supplies regulated 5V power to the board, allowing you to use any USB-supported power source ...