Preguntar and pedir both mean to “ask“, so they are often confusing for English speakers.
1. You use preguntar to show that the subject is asking a question or inquiring about someone or something:
Pregúntale a ese señor dónde está la oficina de correos (Ask that gentleman where is the post office).
Debo preguntar cuándo es la reunión (I must ask when is the appointment).
2. While you use pedir to show that the subject is asking for or requesting something in particular:
Voy a pedir un bolígrafo prestado (I am going to borrow a pen).
Pedimos una copia de los datos de registro (We requested a copy of the registration information).
3. Preguntar is a regular verb, but pedir is quite irregular. Check here its conjugation.
Don’t forget to ask any question you have about this topic with your tutor.