i want to learn git

and

use `git init` 

and add a file named context.txt

`git add context.txt`
and

```
git commit -m "add content",

```

then i modify it,and execute again

```
git commit -m "modify content"

```

and i want to restore previous content,

so execute `git log`

display 

> 
> commit e407bca38f2d609f073516624222d613b7072f71 Author: wyxz125
>  Date: Wed Oct 22 22:21:09 2014 +0800
> 
> 
> 
> ```
> add context
> 
> ```
> 
> 

and `git checkout "e407bca"`
but the content file is not restore previous version...it is still same.,

so what can i do?thanks in advance for any help