Both 以前 and 从前 can be used to refer to the past.
She was a nurse at one time.
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.
Once upon a time there was a rich village.
I used to live with my grandma.
以前 can be used after time words while 从前 cannot.
She usually comes to work before 9:30am.
We were separated two years ago.