Both 以前 and 从前 can be used to refer to the past. 

他从前当过护士。

She was a nurse at one time. 

你以前去过希腊吗？

Have you been to Greece before? 

以前 generally refers to a time before now, can be placed at the beginning or the middle of a sentence ; 

从前 is always used at the very beginning of a story. 

从前有一个富裕的村庄。

Once upon a time there was a rich village. 

我以前跟奶奶住在一起。

I used to live with my grandma. 

以前 can be used after time words while 从前 cannot. 

他通常9点30以前就来上班。

She usually comes to work before 9:30am. 

我们是在两年以前分别的。

We were separated two years ago.