What is the biggest difference with "por" vs. "para"?

Question

When do I use por or para for a sentence?

Answer 1

Por is more of the movement/location question (by, through, around, about) or the "what" of something. Para is more of the "why" or ultimate purpose.

Examples: Estoy aquí por dos horas. I am here for two hours.

Paso por las calles. I am going through the street.

Para empezar, vamos a hablar de estos temas. To start (in order to, or the "why"), we are going to talk about these topics.

No tengo nada para tí. I don´t have anything for you (you is the reason or the "why").

The combined phrases will almost always use "por."

Por supuesto: Of course

Por cierto: By the way

Por lo menos: At least

Overall, "para" is more exact and "por" is more general. Here is an example.

Voy por la ciudad. I am going by/through the city.

Voy para la ciudad. I am going to (for) the city. (The city is the exact location.)

LAST ONE: para mi vs. por mi.

Para mi, los zapatos son más importantes que los calcetines. In my opinion/For me, shoes are more important than socks. (General opinion about something)

Por mi, no importa si vienen o no. By me/Regarding me in this instance, it doesn't matter if they come or not. (Localized opinion in a specific instance: again, localized being the key)