How do you use the word I therefore?

You use it to show the effect of causes.

EX: I laughed at the funeral therefore I was kicked out.

The easiest way to figure if it's the right Word is to replace it with "for that reason"

EX: I laughed at the funeral and for that reason I was kicked out.

The use of the Word therefore will make you seem pompous though so try to not use it unless your paper fits that demographic.