In English we are always asking questions or requesting information.  We may ask for something to be done for us, or desire information about something.   We can ‘ask for’ either.  In Spanish people ask for things just as often.  But in Spanish there are two verbs often used to ask questions.  The verb Peguntar is used to ask for information.  Pedir is used to ask for something to be done or to order something.     The same kind situation exists at least two other times in Spanish. For example, the verbs Ser and Estar mean ‘to be’.  In general, Ser is used to state things that are permanent.  Estar is used to state the condition or location of something.  Then there are Conocer and Saber, ‘to know’.  Conocer is used for knowing people, meeting for the first time, or being familiar with places.  Saber is used to state knowledge of facts.  If you would like to review these verbs take a look at the previous articles “To Be or Not To Be” and “I Know I Know You”.  

Let’s start with Preguntar, to ask for information.  Preguntar is a regular verb.  Its conjugation in all tenses follows the same pattern as other regular verbs, but you still may want to consult your favorite verb conjugation reference. There are plenty of them on-line. 
Also, Preguntar is often used with an indirect object pronoun (me, te, le, les, nos), that indicates TO where the question is going, or FOR whom the question is intended.  You were introduced to indirect object pronouns in the Gustar articles.  
Take a look at some examples of when preguntar is used:
I am going to ask (to) my Dad where he was. – Voy a preguntar(le) a papa dónde estaba.
Can I ask (to) you this.. – Puedo preguntar(le) esto..
She asked (to) him about that yesterday. – Ella le preguntó sobre eso ayer.
Do you want to ask a question? - ¿Quiere hacer una pregunta?
They were asking many questions. – Hacían muchas preguntas.  
We ask (to) her how to do it, (or how is it done). – Le preguntamos como se hace.
We should ask for directions to Panamá City. – Debemos preguntar como se puede llegar a Panamá. (how does one arrive to Panamá). 
Ask (to) her how long she has been here. – Pregúnta(le) cuanto tiempo hace que ha estado aquí.  
Also, Preguntar is sometimes used with the preposition por.  If you want to ask for, or about someone or something, or ask a question on someone’s behalf, you can use preguntar por:
She should ask (to) them about her car because it has not arrived yet. – Debe preguntar(les) por su carro porque no ha llegado todavía.
I want to ask a question for (on behalf of) Jamuna. – Quiero hacer una pregunta por Jamuna.  
Now lets look at Pedir, to ask for something to be done, or to order something.  Pedir is not a regular verb.  But it is not an irregular verb either.  Pedir has some differences to regular verb patterns, but only in a few cases.  Do review the conjugations of Pedir in your Spanish verb reference.  Pedir in some cases will also use an indirect object pronoun.  
He is asking too much money for the house. – Pide demasiado dinero por la casa.
I want to order eggs for breakfast. – Quiero pedir huevos para el desayuno
Where is my order? – ¿Dónde está pedido?
I always ask (to) her to wash the dishes. –  Siempre le pido que lave los platos. (subjunctive).
She already ordered lunch. – Ya pedió almuerzo.
We asked (to) the bank for a loan. – Le pedimos al banco un préstamo.  
When I ask (to) her to clean, she does it well. – Cuando le pido que limpie, ella lo hace bien.
Keep in mind that Pedir means to ask for.  The ‘for’ is already included in Pedir.  
I already asked for it. – Ya lo pedí.
Of course, sometimes when asking for something, Preguntar and Pedir are not used.  It just depends on the context of the sentence.  For example,  ¿Puede hacerme un favor?  Can you do me a favor?  Or ¿Donde está María? Where is María? Asking for a favor is a request for something to be done.  Asking where Maria is, is a request for information.  But when sentences arise like the above examples calling for Preguntar or Pedir, you need to know which one to use.
If you are living in or visiting a Spanish speaking country, the importance of being able to ask for something or being able to request information is obvious.   Knowing the difference between Preguntar and Pedir will allow you to Ask for information, or for something to be done (and hopefully you will Receive it), like a true Spanish speaker.  Lucky for us it is a pretty straightforward concept.
altHope this helps!