Here is a detailed guide on how to get started with ATMega328P microcontroller. The guide goes in details on how to setup it on a breadboard and how to upload your first code on it. and blink a led.
The real benefit of using this microcontroller is that it’s only $4 US, whereas many other micro-controllers are 10X that price. It can also be easily programmed in the universal programming language, C++. The ATMega is also equipped with a decent amount of memory for any project.
Getting Started With the ATMega328P – [Link]