The path to become a Permanent Resident or Green Card holder in the USA is quite a complex and long process. Depending on the current status that you are in, the prospective Green Card applicant has lots of different options.
The first and most informative website that I can think of among many others is the US Citizenship and Immigrations Services web site (uscis.gov). There is a seperate link called Getting Green Cards. This has loads of excellent information and very easy to follow.
Then there is lot of good Immigration websites and of course many Immigration Attorneys. For a complex process of going thru the Green Card I would highly recommend that one goes thru the services of a good Immigration Attorney or a Law firm which specializes in US Immigration. Using the Internet one can search for Immigration websites as well as Attorneys.
Just like any other major lifes decision, the path to getting a Green Card and the steps to follow is a very critical decision one has to make. Thus it is essential that proper research and sound legal advise is availed to minimize problems.
Please note that I am neither a qualified Immigration Attorney nor qualified to make any suggestions. My review is only to give very basic general information.