whats the difference between fate stay night fate/zero?

is fate/zero part of fate stay night or is it a complete different anime as i already watched fate stay night havent heard of fate zero some people say it is or are they just similar.

Tangi2020-06-18T12:51:25Z

If you've watched F/SN, you know that Shirô was adopted and raised by a mage who did it out of regret for the destruction he made in the previous grail war.
You also know that Gilgamesh is a servant who gained a new life during a grail war. Or at least you've wondered why there are two archer class servants.

Fate/Zero is the story of this grail war.

F/Z is less focused on one character like F/SN, and follows all 7 masters and their servants.

Entropy2020-06-18T12:31:33Z

Fate/Zero is a prequel to Fate/Stay Night.  Zero happens 10 years before Stay Night.  I liked Zero better.  They do have ALOT of similarities.