Q:

Can't add file to github with git bash

I have created a Github repository and I'm trying to add a simple text file to that repository. 
This file is inside a folder with the same name of the repository. 
This is the first time I'm using Github and I've searched other similar questions but couldn't find an answer. 
So, using Git bash, I navigate to the folder and type:
git add texto.txt
git commit -m "first commit"
git push origin master

But the file is not uploaded, and I see the error:
git@github.com: Permission denied (public key) 
fatal: Could not read from remote repository. 
Please make sure you have the correct access rights
and the repository exists. 

I have created a SSH/RSA key in my PC here:
C:/Users/xxxxxx/.ssh/id_rsa

I know this should be simple, but for sure I'm doing something wrong here..

A:

Git add is the first step to make Git aware of a file. 
Your next step is to git commit to create a snapshot of your files (your commit can contain multiple changes you added)
The final step is to git push the changes to github. 
The add makes git aware of your changes.  commit bundles one or more changes into a snapshot.  push pushes one or more commits to another git repository.  
I highly recommend going through a getting started tutorial:

https://git-scm.com/book/en/v2
https://www.youtube.com/watch?v=0fKg7e37bQE

