Para

Destination

Para describes the destination or time by which something will happen.

  • Tomaron el tren para Córdoba. They took the train for Cordoba (destination).
  • Los chicos salieron para el colegio. They left for school (destination). 
  • Terminaré para martes. I'll finish it by Tuesday (time by which it'll occur)

Goal

This can be summarized as "in order to"

  • Estudio para tener éxito. I study in order to be successful.
  • Trabajo para mejorar mi español. I work in order to improve my Spanish

Comparison

  • Para médica, sabe poco. For a doctor, she doesn't know much.
  • Por un profesor, tiene poca paciencia. For a teacher, he doesn't have much patience

Opinion

  • Para mi, tenis es el mejor deporte. In my opinion, tennis is the best sport.
  • Para el, cuesta mucho. In his opinion, it costs a lot.

Employment

  • Trabajo para Sr. Dominguez. I work for Mr. Dominguez (he's my boss).

Expressions

There are many common expressions that use para

  • para entonces by that time
  • para otra vez for another occasion
  • para siempre forever
  • para variar just for a change
  • ser tal para cual to be two of a kind

Por

Through

  • Salga por esa puerta. Go out through that door.
  • Yo fui por el bosque para encontrar el tesoro. I went through (por) the forest in order to (para) find the treasure.

Around

  • por acá/aquí/ahí/allá around here/here/there/there
  • Hay muchos restaurantes por este calle. There are many restaurants on (around) this street.

Duration/Imprecise Point in Time

This is contrasted with para, which is used when there is a specific date, like Tuesday.

  • Trabajé por muchos años.  I worked for many years
  • Nos veremos por Navidad. We'll see each other around Christmas

Cause or Reason

This is different from a "goal". Both por and para answer "why?" in this case,  but para is more like "he did this with the purpose of ...", but por means "this happened because"

  • Él murió por falta de agua. He died for lack of water.
  • Se ofenden por cualquier cosa. They get insulted over anything.
  • Te felicito por tus buenas notas. I congratule you on your good grades.

Means by which something is done

  • Yo mandé un mensaje por correo electrónico a mi amigo. I sent a message by e-mail to my friend.
  • Me gusta hablar por telefono.  I like to talk on the phone

Motivation

Once again, this is very similar to "Cause or Reason" and "Purpose". This is used for the person or people whose sake something is done.

  • Brindaron por el equipo vencedor. They toasted for the winning team. 
  • Todo lo hice por mi familia. Everything I did was for my family. 
  • No voté por nadie.  I didn't vote for anyone. 

Exchange/Substitution

  • Pagué mucho por mi computadora. I paid a lot for my computer
  • Yo enseñé la clase por el profesor.  I taught the class for the professor  (instead of him).

By

  • El libro fu escrito por un historiador. The book was written by a historian.

Note: Sra. Cuadrado says you should use "de" instead of "por"

Helper word

Motion

Por adds the idea of motion to prepositions of location. It's a helper word.

  • El caballo saltó por encima de la valla. The horse jumped over the hurdle
  • El mozo pasó por detrás de las sillas. The waiter passed behind the chairs.

Be careful

  • Yo trabajo por John. I work for John (in his place).
  • Yo trabajo para John. I work for John (he's my boss).

Source

Repaso, p. 484-487