Confusion with Prepositions

xxxI would like to know the right use of the prepositions . Because I have many doubts about the use of by. for, in, on. etc. I am native spanish speaker, and in spanish we use the same prepositions in differents cases.
Thanks.

[A.Russell]

That's quite a large subject to cover in a post. You are best to get a good grammar dictionary for reference and practice a lot.

[Tdol]

They have many different uses- for location, time, with verbs, etc. Could you give a more specific example of what confuses you?

Originally Posted by tdol

They have many different uses- for location, time, with verbs, etc. Could you give a more specific example of what confuses you?

I have confusion with the use of "by and for"
thanks

[Tdol]

With time:

By- marks the limit- the end of the time period:
I want this work finished by Friday. (You can finish before Friday, but Friday is the last day)
For- the duration (how long)
I worked for six hours without a break.


BTW- There's a lot of practice here: http://www.usingenglish.com/quizzes/