Proper use of the prepositions por and para can be difficult for non-native Spanish speakers because of their variety of meanings. Both of them usually mean "for". Let's focus on their uses to truly grasp por vs para.
Use por to indicate reason or motive:
Estoy aquí por asuntos de negocios.
I am here because of (for) business reasons.
Use por when discussing time or day:
Hago la tarea por las noches.
I do homework at night (for nights).
Use por when expressing exchange:
Te doy mis palabras por tu dinero.
I give you my words for your money.
Use para to indicate purpose or use :
Sonia va al supermercado para comprar el pan.
Sonia goes to the grocery store in order (for) to buy the bread.
Use para to express destination: recipient (a person):
María va a comprar un regalo para él.
Mary is going to buy a gift for him.
Use para to express destination: location (a place):
¿A qué hora parte un tren para Berlín?
What time does a train leave for Berlin?
Use para to show use:
Aquí hay un lápiz de color para colorear.
Here is a colored pencil for coloring.
Use para for specific time:
Sólo para el año nuevo.
Only for New Years Eve.
Use para to say being:
Es muy caro para un anillo.
It is very expensive for a ring.
Use por for a place or an area:
Está por el barrio.
It's for (around) the neighborhood.
Use por to express per:
Puede tener una hora por día como máximo.
You can have one hour for (per) day maximum.
Use por to express passive voice:
El taxi es conducido por Juan.
The taxi is driven by Juan.
Use por with manner, means of:
Ellos vienen por tren.
They come for (by) train.
Use por with price:
¿Cuánto cobran por noche?
How much do you all charge for (per) night?
Use por with verbs like ir, enviar, venir, etc.:
La comisión por enviar el dinero es de veinte dólares.
The fee for sending the money is $20.
Use para for opinion:
Para mí, el color del coche es muy importante.
For me (in my opinion), the color of the car is very important.
Use para to say for:
Sí, un medicamento para la gripe.
Yes, a medicine for a cold.
By the time you finish this lesson, por vs para will no longer be a dilemma for you!
Por vs Para - Quick Explanation
The prepositions por and para tend to be troublesome for non-native Spanish speakers. In some cases this is due to the fact that each of them is sometimes equivalent to the English preposition for. In other cases the difficulty comes from the diverse uses that each one has. For example:
Yo no sé si María tiene el dinero para comprar los boletos.
I don't know if Mary has the money to buy the tickets.
María va a comprar un regalo para ellos.
María is going to buy a present for them.
Estoy aquí por asuntos de negocios.
I'm here for business issues.
Estoy aquí por dos semanas.
I'm here for two weeks.
Uses of the preposition Para
"In order to" and the expression of purpose or use
To indicate destination (location or recipient)
Voy para Oaxaca.
I am going to Oaxaca.
Salimos para la tienda a las doce.
We left for the store at twelve.
Estos zapatos son para Miguel.
These shoes are for Miguel.
To convey the time limit (deadline) of a particular action
considering (that)
Para alguien tan inteligente, lo que hizo es mediocre.
For (considering that) somebody as smart as he is, what he did was mediocre.
To express suitability
To express the idea of "in my opinion"
Para mí, el carro verde es mejor.
In my opinion, the green car is better.
Para Luis, el rojo es el máximo.
In Luis's opinion, the red one is the best.
Uses of the preposition Por
To express the reason or motive for an action
Lo hice por tí.
I did it for you.
Cancelaron el partido por la lluvia.
They cancelled the game because of the rain.
Austin es conocido por su música.
Austin is known for its music.
To indicate a place where movement is occurring (through)
Periods of time: parts of the day
por la mañana - in the morning
por la tarde - in the afternoon
por la noche - in the evening
por la noche - at night
por la madrugada - in the early morning
Por = per
Estoy contigo cien por ciento.
I'm with you one hundred percent.
Íbamos a 80 millas por hora.
We were going 80 miles per hour.
Gano diez dólares por hora.
I make ten dollars per hour.
To express price or an exchange
Por + manner or means of transportation
agent of passive voice Por = by
Esa canción fue escrita por Tracy Chapman.
That song was written by Tracy Chapman.
the object of an errand with verbs like: ir, enviar, mandar, venir, etc.
with "estar" to express "to be about to"
Mi papá está por explotar.
My dad is about to explode.