when safari is closed does it still use resources?

Not if you remove it by clicking twice on the Home button then sliding it out of the list of running apps. Apps that are idle in the background do use resources but less than when active in the foreground. This is true for all apps.

For the most part, apps other than the one your currently using are in a suspended state. Perhaps if you explained why you're asking, someone could give you additional relevant information.

Best of luck.