Git is a version control system. Git is free software. A good tutorial can be found at http://www.liaoxuefeng.com/wiki/0013739516305929606dd18361248578c67b8067c8c017b000/0013743256916071d599b3aed534aaab22a0db6c4e07fd0000 frequently used command: 1 git init 2 git add <file> 3 git commit -m "my explanations" 4 git status : check out status of the repository 5 git diff <filename>: check out what is changed in the repository 6 git log : list the history of commit (version) 7 git checkout -- file : delet changes since last add or commit 8 git reset HEAD file : unstage file to version of last commit(current version) 9 git reset --hard HEAD^ : go back to the last version. git reset --hard HEAD^^ : go back to the previous previous version. git reset --hard HEAD~100 : go back to the 100th previous version. 8 git reflog: check out history of git command.