I think you might have a hard time finding someone who can explain how to implement irradiance calculations (or approximations thereof) to a 3 year old. If you are serious about implementing your own renderer, then you need to understand how it works. Have you read any books on the topic? Are you willing to put in the effort to implement and debug the system?
If not, then why not just use something like UE4 or Unity? If so, then start digging in to the resources available - there is lots of info on YouTube with explanations, so try to go as far as you can on your own before asking someone to explain the whole thing to you. If you get stuck on a specific piece, then there are lots of people here to help!