The Spanish prepositions por and para have different meanings, but they are often confused. In this article, you will learn some of the most frequent uses of these prepositions.

Reason v. Purpose
One of the most common uses of the prepositions por and para is to explain our reason for doing something.
A very simple example to understand the difference between these two prepositions is to answer the typical question "Why are you learning Spanish?" Probably the first thing that comes to mind is to answer with "Because..." ("Because I like languages," for example). However, whenever we are interested in learning someone's reason for something, the answer may involve using por and para.
For example, "¿Por qué quieres aprender español?" "Para viajar," "Por la cultura," "Para hacer amigos de otros países," "Por mi trabajo," "Por diversión," "Para estudiar en el extranjero," ("Why do you want to learn Spanish?" "To travel," "For culture," "To make friends from other countries," "For my job," "For fun," "To study abroad"), etc. As you will note, the reasons for studying Spanish are quite varied, but the most important thing is that they are expressed in two different ways:

We use por when we are talking about the reason or cause for a given action or situation. For example,
Llegué tarde por el tráfico - I got there late due to the traffic
China es famosa por su comida - China is famous for its food
We use para when we are referring to the purpose or goal of a given action. For example,
Trabajo para ganar dinero - I work in order to earn money
Ella estudia para ser doctora - She is studying to become a doctor
Uses of POR
Cause or reason
Brindemos por tu cumpleaños - Let's drink a toast to your birthday
Tomo clases de baile por diversión - She is taking dance classes for fun
Period of time
Estudié en Australia por diez meses - I studied in Australia for ten months
Jugamos futbol por dos horas - We played football for two hours
Approximate location
Ayer pasé por tu casa - I came by your house yesterday
En un mes estaré por la playa - I will be at the beach in one month
Means
Mándame el informe por correo electrónico - Send me the report by email
Hablamos por teléfono - We spoke on the telephone
Part of the day
Mi novia y yo salimos a correr por las mañanas - My girlfriend and I go running in the morning
Estudio español por las noches - I study Spanish in the evening
Speed
La velocidad máxima permitida es 110 kilómetros por hora - The maximum speed limit is 110 kilometers an hour