In Ardino Uno, my issues regarding Atmega 328/P and its basics
My question is that it is specified by Atmel that its Atmega 328/P is a picoPower device. So my question is in what respect the term picoPower is used by Atmel in regards of Atmega 328/P?
And my second queston is how a microcontrollers can be run at different speeds?
PicoPower - is a technology from Atmel for reducing MCU power consumption. It is achieved by various techniques both from hardware (IC design) and tuning from the firmware (clock prescaling, switching off unused blocks etc).
I recommend you to view their appnote about picoPower and how to use it. It also has info about clock prescaling. picoPower Basics