Derek, when it comes to 'para' and 'por', don't think about English translations -- it's like nailing Jell-O to a wall. Instead, visualize what these prepositions represent in terms of movement and position in space: 'Para' is movement from point A to point B. For example, 'Este regalo es para tí', or, 'Voy para la casa'. 'Por' represents movement through a conduit, such as street, tunnel, path, or even through time. For example, 'Camino por la calle', 'Manejo por el túnel', 'Corro por el lago', or 'Estaba en México por dos días'. Even the phrase 'por favor' represents movement through a conduit, albeit abstract. When I say 'please', I'm asking you to do it via the "favor route". I have created an actual visualization of this on my blog which you can see here: http://www.tonymarshmethod.com/blog/2014/12/12/por-and-para-solved

Thanks a lot, Sergio. You translated all of them for me~~~Best wishes from China. I guess I'll have lots of questions in the future, please do leave me a message here when you are convenient.

1- They say that the new building would be finished at the end of the next year. (You should use "para finales del próximo año") 2- Barcelona won against Real Madrid 2 by 0 "Por" here means "by" It can be used to compare things or to multiply numbers 3- We must buy a new bike for the vacations You must use "para" here if you want to say for the vacations (because you want to use it on vacations) You must use "por" here if you want to say for the vacations (because the reason that you buy a bike is that vacations are coming) 4- It was difficult to enter for me and when I finally did it there were no one. Hope this can be useful for you!