Understand where you are starting from
Understand from where you are starting
not sure which is correct

Without context, it is difficult to provide a sensible answer to this one.

As a rule, you should try to avoid ending a sentence with a preposition ('from' in your example). This is a throwback from Latin, and many people do not consider this a grammar ruling nowadays.

However, as there are still a number of people who do adhere to this rule, I would advise sticking with it. That said, if rewording your sentence makes it sound too contrived, then leave your sentence as it is with the preposition at the end. If these are spoken words, as opposed to written text, then definitely leave the preposition at the end (i.e. your first example).

I hope that helps

Craig