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What is the correct way to use 'para' in Portuguese?

"Para" in portuguese is like "to" in some phrases in English. For example: "They go to school next year" . The tranlation is: "Eles vão para a escola no próximo ano".
So, "para" is a proposition of direction and motion. In some English phrases the preposition "to" isn't used, like in "He is going home". But, in portuguese, "para" is allways used: "Ele está indo para casa".

"Pela" is the contraction of "por" + "a". "Por" is like "by" and "a" is the definite article "the" in the female form. Example: "Joan passed by the girl without seeing her". In portuguese:"Joan passou pela garota sem vê-la". Did you understand?

Concordo com pienkovski 2 e adicionalmente em Português “para” pode ser referente a to, for, in, onto,toward,towards,about to, in order to ou ainda a terceira pessoa do verbo parar, vai depender apenas do contexto

I think with this example, you should can see better:
This is the most usual:
"Estou indo PARA a praia" , "I´m going TO the beach"
"PARA você?","FOR you?"
important:
PÁRA!!!" com acento, It´s like "STOP THIS!!!" verb (parar - to stop)

para has a transitive sense...

para você (to you) - it's moving from someone else till you.
para fazer isso (in order to do that) - changing from the previous situtation to the next one.

por has an instrumental or motivational sense...

por você (because of you) - you are the reason of why I'm doing something.
por isto (because of this) - this is the cause of the mentioned effect.
por este meio (by this mean) - through this mean, I do something.

pelo/pela were "porlo / porla" in the past. They are in fact the union between "por" and an article "o / a".

Look at this:

Por o caminho....
(some centuries past till it became)
Porlo caminho...
(more centuries past and now we have)
Pelo caminho.

It follows our general rule of gender and number:
pelo / pela
pelos / pelas

Pelo menos agora você tem um meio para estudar por mim! ;D