If you are using Windows, than simply use github Desktop for windows:
https://desktop.github.com/
It works pretty simple. I am not an Git expert, but can do a few things. I do google a lot to remember more advanced things like yesterday I merged 5 partial commits into one, before I issued a Pull Request (USBHost_T36).
If you are simply creating your own stuff, you typically can simply create a new project and then push it up to github as the master branch.
If you are wanting to make updates to be pulled into some other projects like: Core or USBHost... It is not too difficult:
Sometimes depending on what you wish to do: Simply look at or use someone elses project:
a) Go to github... to the project you wish to download to your machine and up there example:
https://github.com/PaulStoffregen/cores
There you will see a Clone or download button (green), you can go to the clone in desktop button, which should bring up the github desktop app, which allows you to choose where to put it on your machine...
b) If you are going to want to make changes, when looking at Pauls project up on github, you should click on the FORK button near upper right, which will create a fork of it in your Github account. From there you can clone in desktop to get it to your machine...
If you are making changes to other persons projects, what I do is SYNC my fork of the project up to the master version (more on this if interested). Then for the change, I create a new BRANCH of the project, I then make my changes in the new branch and push them up to github. When you are happy with your changes, you can issue a Pull Request (In the branch menu), which should generate the Pull request on github. When the change is accepted, you receive email, from which you can then close out your temporary branch and sync back your main branch to the master...