How do i know how to use the 为? I want to know how to use the 为, because there are cases where we dont translate it and it gets it harder so i'd like like to know the uses and effects this one provoke in the sentence.
I am no grammar expert, but let me attempt an answer based on my level of attainment. I am sure others could do better.

This is one of the most commonly occurring and useful word in the Chinese language, just about behind 的 &amp; 了。 

The problem is, (just like 的 &amp; 了), it is a preposition, and when used in combination it becomes a verb, a conjunction, an interrogative, (a sentence of inquiry that asks for a reply)

So it is in an actual sentence that its usages become apparent.

As a preposition it is "for"; 他的牺牲是为了什么?, (his sacrifice is for what?)

As a conjunction it is "because of"; 他为爱国以牺牲了生命, (Because of his love for country he sacrificed his life)

As a verb -- 成为 -- "become"; 他的牺牲将会成为传说, (His sacrifice would become a legend)

As an interrogative -- 为什么, "why", 他为什么牺牲自己的生命?, (why did he sacrifice his own life?)