A fact is something that is true.
 Facts are something that you can prove to be true.

Fact!
There are nine planets in our solar system.

Fact!
The earth is the third planet from the sun.

These are facts that we can prove to be true. 
The answer will always be the same.

An opinion is something that you
think or feel.
Opinions are usually people's ideas or tell the 
way they feel about something.

Opinion!
Saturn is my favorite planet.

Opinion!
I think they will discover life on Saturn someday.

Not everyone believes Saturn is the best planet.  
This is someone's opinion or belief. It is just what 
someone thinks or feels.