Para que is generally used as "So that" as well as "For what purpose?"
1) "Para" and "para que" both mean "in order to" or "so that", but you cannot use whichever one you feel like. When you have the same subject the entire way through the sentence, use "para".
e.g. I am here so that I can study (or - I am here in order to study) - "Estoy aquí para estudiar".
She needs a towel so that she can clean the counter (or - she needs a towel in order to clean the counter) - "Ella necesita una toalla para limpiar la encimera"
However, with a change of subject you must use "para que" plus subjunctive. (The "que" introduces the change of subject).
e.g. : I am here so that you can talk to me - Estoy aquí para que me hablen
She needs to help so that he can leave - (Ella) necesita ayudar para que salga (él).
2) Although both para qué and por qué in questions usually can be translated as "why," there is a subtle difference in meaning between them.
One way of thinking about the difference is that in por qué questions the speaker is seeking to know the cause of something, while para qué questions focus on the purpose or intention of something. There is an overlap, and it is often possible to substitute por qué for para qué, but not always the other way around. Whereas the question ¿por que? might be thought of as "Why?" the question ¿para qué? might be thought of as "What for?"
¿Por qué murió el soldado? (What caused the soldier to die?)
¿Para qué murió el soldado? (For what purpose did the soldier die?)
¿Por qué ganó la elección? (What caused her to win the election?)
¿Para qué ganó la elección? (For what purpose did she win the election?)
¿Por qué es eso? (Why is that?)
¿Para qué es eso? (What's that for?)