When to use para before infinitive
This continuously confuses me and I have never heard/read the actual rule. I don't know how to explain the question very well but I think examples will show you what I mean. I'm writing an email to someone and want to say "I went to the office to ask about my luggage". The first part is simple: "Fui a la oficina"... but then to say "to ask", do you say "preguntar" or "para preguntar"? Preguntar literally translates as "to ask", but I've seen para used before the infinitive (sometimes) in situations like this, and it also seems better to say "para preguntar" for some reason. There are endless situations like this that I've run into, this isn't an isolated question. Another example would be "I'm going to the store to buy some apples" - "Voy a la tienda comprar unas manzanas" or "Voy a la tienda para comprar unas manzanas"?
Actually now that I read over my question I'm wondering about the second half of my first example: is it correct to say "sobre mi equipaje" (sobre is the direct translation of 'about') or is it better to use "para" or another word here?
In some cases, you can think of "para" as being equivalent to the English "in order to."
Voy al mercado para comprar varias cosas.
I'm going to the market in order to buy several things.
Mi amigo me llamó para hablar de la fiesta.
My friend called me in order to talk about the party.
This would hold true in your sentence: I'm going to the office in order to ask about my luggage.