I would like to know how to give groups/users permissions to specific folders only in sharepoint 2010?
Navigate to the document library with the folders. Tick the little check box beside the folder in question. In the ribbon, there should be an option for Manage Permissions. From there you will have to break the permissions inheritance (there should be a link or option called Edit permissions). Once the inheritance is broken, you can add or remove people as needed.
Steps may not be 100% accurate since I'm going from memory on 2010.