In my SharePoint 2013 environment I have configured Search service and I have following questions:

1- I need to search only one site collection but the default content source searched the entire web application consisting of all other site collections.How can I restrict it to one site collection only as it is taking lots of disk space as well and its not required.

2- I have a document library and it has folders, when I try to search the files inside the folders, I dont get any results even after full crawl. So Is there something to search within the folders that I need to configure.

Please suggest something and thank you in advance.