What I learned today

I learn that compound sentence is a sentence that made of to simple sentence.

Example.

I tried to play baseball, my friend Chung tried to play Basketball.

Also after that I learn complex sentences.

Example.

When that parents come home children, all sit down quietly.

What I learned today

Today in ESL I learned about sentence. Three things that complete sentence must have is subject, predicate and a complete thoughts. A sentence fragment is the sentence that have no complete thought, subject and predicate.
The Example of a fragment is:

Is very big

It is a fragment because it have no complete thought and no subject.