1. 新建一个文件：Untracked files
2. 修改一个文件：Changes not stages for commit
3. 运行命令git add 之后：Changes to be committed
4. git commit 提交代码

撤销修改：

• 撤销add：git reset HEAD <file>或git reset HEAD –
• 从Changes to be committed到Untracked files：git checkout .或git checkout –<file>
• 撤销commit 到add之后：git reset --soft HEAD^
• 撤销commit 到add之前：git reset HEAD^