Common Words:
* Puerta: Door
* Para: For
* Pero: But
* Porque: Because
* Poder: To be able to
* Primero: First
* Poco: Little, a little
* Padre: Father
* Palabras: Words
* Pan: Bread
Slightly Less Common, but Still Useful:
* País: Country
* Parte: Part
* Pasar: To pass, to happen
* Pensar: To think
* Perro: Dog
* Peso: Weight, Peso (currency)
* Playa: Beach
* Plátano: Banana
* Pregunta: Question
* Precio: Price
More Advanced/Specific Vocabulary:
* Paciencia: Patience
* Participación: Participation
* Perfecto: Perfect
* Problema: Problem
* Probar: To try, to taste
* Proyecto: Project
* Pintura: Painting
This is just a small sample, of course. The Spanish language has thousands of words starting with "p"! The frequency of use will vary depending on context.