Hi everbody,

I've read a thread about Prepositions in Questions in this forum.
Now I have some questions:

The given example was:
What is a pen (used) for?

The question was:
"I would like to know when I am supposed to do this, why and how?"

The given explanation was:
"If a word like for comes after the word it modifies, it's part of that word, and so it doesn't move unless the word it modifies also moves.
For doesn't move with what because for does not modify what. It modifies used. Used for is a set phrase.
For is a particle not a preposition."

My question:
Everything is well explained so far, but I can't find any examples where the opposite is right, means prepositions which modifie nouns or which are not particles of a verb.
Can you please give me some examples for this, because the most easiest rule (and I'm unsure whether it's right or not) which I created out of this is "the preposition stays always with the verb and at the end of the sentence/question."