Generating PDF- environment.rb problem



I would like to implement a PDF function into my application.
I have already installed the pdf-writer-1.1.6.

Firstly, there are several folders in this zip folder e.g. pdf, writer
Where exactly should I paste this folders to?

Secondly, I added the following codes to the environment.rb:
require ‘pdf/writer’
Mime:Type.register ‘application/pdf’,:pdf

Where should I place these codes and the should the word “application”
be replaced with my project’s name?
I am sure that there is something wrong with the codes in here as when i
restarted WEBRICK in my command prompt, some of the errors that occurred

  • already initialized constant OPTIONS
    -no such file to load – transaction/simple

Can someone please give me a solution? Because there is no way I can
implement the codes if I cannot start my WEBrick successfully.
This is quite urgent as the deadline is drawing nearer. Please help!
Thank you very much!!!