Which, Who ,That(Used in which case) Run on sentences:

In modern speech, which refers only to things. Who (or its forms whom and whose) refers only to people. That normally refers to things but it may refer to a class or type of person.
http://englishplus.com/grammar/00000255.htm
Example: I want the ball that was used in the World Cup.
That was the one who owned the house
The girl which needed the math book was looking for it.
A run-on sentence is a sentence in which two or more independent clauses (i.e., complete sentences) are joined without appropriate punctuation or conjunction
http://en.wikipedia.org/wiki/Run-on_sentence
The girl ate pizza then she went home.
The girl ate pizza. Then she went home.