How can I change access permissions from the command line?

A. A utility called CACLS.EXE comes as standard with NT, and can be used from the command prompt. Read the help with the CACLS.EXE program (cacls /?). To give user john read access to a directory called files enter:
CACLS files /e /p john:r
/e is used to edit the ACL instead of replacing it, therefore other permissions on the directory will be kept. /p sets permission for user: