que versus por versus para
Please explain and compare: Tengo que pagar el coche hoy
Mi hermano no quiere pagar por el hotel
Esas fresas son para comer
"In Spanish, The key to understanding which preposition to use is to think of the meaning you want to convey. If I use a phrase such as "three for a dollar" in English, the "for" has a different meaning than it does in "this book is for you." In the first case, "for" indicates an exchange or a rate, while in the second case it indicates an intention or direction. Thus the Spanish translation of the two phrases are different, "tres por un dólar" and "este libro es para ti." - http://spanish.about.com/cs/grammar/a/porpara.htm
Que is one of the most difficult words in Spanish, even for many native students to understand. It could be a linking word, as in the sentence you have written, a pronoun and some other things. In that sentence, it just stablish a relationship between the main clause "(Yo) Tengo + DO" and the object (what you have to do in this case) "que pagar el coche".