course link: https://www.liaoxuefeng.com/wiki/896043488029600 , super easy and simple course, you can use google translator.
you can use jit GUI but cmd line is more straight forward, unless you have complex tree to view: https://www.syntevo.com/smartgit/download/
Since Aug 2021 we can't use passwd but personal token to push: https://docs.github.com/en/authentication/keeping-your-account-and-data-secure/creating-a-personal-access-token
after that I can clone: git clone https://github.com/jdai/learnjit , then use cloned repository for further developing - add/commit
$ git reset --hard HEAD (going back to HEAD)
$ git reset --hard HEAD^ (going back to the commit before HEAD)
$ git reset --hard HEAD1 (equivalent to "^")
$ git reset --hard HEAD2 (going back two commits before HEAD)