How to create gmail chrome extension?

I have started learning how to create a chrome extension and there are plenty of video tutorials on YouTube for creating basic chrome extension but I want to create something useful such as a chrome extension for Gmail which can scan your email and show you the number of email send and received by every person or Facebook extension where I can see all the notification and reply from there without even going to facebook.com.

About me technical knowledge: I am basically a beginner and just know some basic html and css stuff a bit of jquery.

I have look around on the internet but I couldn't find any tutorial about these so please can anyone of you help me with this. I have tried reading Google and Facebook API documentation but honestly everything gone over my head.

Basically I cant able to make sense from the documentation and how to use them.

Can any one please help me with this!