There's nothing special about chmod, you always need to name a file correctly to refer to it,
so if its not in the current directory you'll have to give a relative or absolute path, or else
cd to the relevant directory.
If you want to see the permissions of files use "ls -l"
The r,w,x flags mean read, write and execute. The three groups are for owner, group, world,
so -rwxrw-r-- means read/write/execute for the file's owner, read/write for file's group members
and only read for the rest of the world (other users). Root always has all privileges.