To manage file or directory permission:

To manage file or directory permission:

To see files and directories:
ls

To see files and directories (With details):
ls -l

chmod = Change mode or permission of any file or directory

r = Read
w = Write
x = Execute
l = Link/Symbolic link/Symlink (Related or a shortcut of any other file or directory)
d = Directory (Represent directory)
D = Door (Not common on Linux systems, but has been ported)

u = User
g = Group
o = Others

WITH WRITE AND EXECUTE PERMISSIONS AND WITHOUT READ PERMISSIONS:

--wx-wx-wx = Represents write and execute permission of a file (With owner, group, and others permissions)

d-wx-wx-wx = Represents write and execute permission of a directory (With owner, group, and others permissions)

l-wx-wx-wx = Represents write and execute permission of a file or directory related or a shortcut of any other file or directory (With owner, group, and others permissions)

WITH READ AND EXECUTE PERMISSIONS AND WITHOUT WRITE PERMISSIONS:

-r-xr-xr-x = Represents read and execute permission of a file (With owner, group, and others permissions)

dr-xr-xr-x = Represents read and execute permission of a directory (With owner, group, and others permissions)

lr-xr-xr-x = Represents read and execute permission of a file or directory related or a shortcut of any other file or directory (With owner, group, and others permissions)

WITH READ AND WRITE PERMISSIONS AND WITHOUT EXECUTE PERMISSIONS:

-rw-rw-rw- = Represents read and write permission of a file (With owner, group, and others permissions)

drwx-rw-rw- = Represents read and write permission of a directory (With owner, group, and others permissions)

lrw-rw-rw- = Represents read and write permission of a file or directory related or a shortcut of any other file or directory (With owner, group, and others permissions)

WITH GROUP AND OTHERS PERMISSIONS AND WITHOUT USER PERMISSIONS:

----rwxrwx = Represents read, write, and execute permission of a file (With group and others permissions)

d---rwxrwx = Represents read, write, and execute permission of a directory (With group and others permissions)

l---rwxrwx = Represents read, write, and execute permission of a file or directory related or a shortcut of any other file or directory (With group and others permissions)

WITH USER AND OTHERS PERMISSIONS AND WITHOUT GROUP PERMISSIONS:

-rwx---rwx = Represents read, write, and execute permission of a file (With owner, and others permissions)

drwx---rwx = Represents read, write, and execute permission of a directory (With owner, and others permissions)

lrwx---rwx = Represents read, write, and execute permission of a file or directory related or a shortcut of any other file or directory (With owner and others permissions)

WITH USER AND GROUP PERMISSIONS WITHOUT OTHERS PERMISSIONS:

-rwxrwx--- = Represents read, write, and execute permission of a file (With owner and group permissions)

drwxrwx--- = Represents read, write, and execute permission of a directory (With owner and group permissions)

lrwxrwx--- = Represents read, write, and execute permission of a file or directory related or a shortcut of any other file or directory (With owner and group permissions)

WITH ALL THE PERMISSIONS OF READ, WRITE, AND EXECUTE ALONG WITH (USER, GROUP, AND OTHERS):

-rwxrwxrwx = Represents read, write, and execute permission of a file (With owner, group, and otherS permissions)

drwxrwxrwx = Represents read, write, and execute permission of a directory (With owner, group, and others permissions)

lrwxrwxrwx = Represents read, write, and execute permission of a file or directory related or a shortcut of any other file or directory (With owner, group, and others permissions)


NO ANY PERMISSIONS:
---------- =  Represents without any permission of a file
d--------- = Represents without any permission of a directory
l--------- = Represents without any permission of a file or a directory related or a shortcut of any other file or directory

Actions

To add:

To add readable permission to any file or directory:
chmod +r [FILE_NAME_OR_DIRECTORY_NAME_OR_PATH]

To add writable permission to any file or directory:
chmod +w [[FILE_NAME_OR_DIRECTORY_NAME_OR_PATH]

To add executable permission to any file or directory:
chmod +x [FILE_NAME_OR_DIRECTORY_NAME_OR_PATH]

To add readable and writable permissions to any file or directory:
chmod +rw [FILE_NAME_OR_DIRECTORY_NAME_OR_PATH]

To add readable and executable permissions to any file or directory:
chmod +rx [FILE_NAME_OR_DIRECTORY_NAME_OR_PATH]

To add writable and executable permissions to any file or directory:
chmod +wx [FILE_NAME_OR_DIRECTORY_NAME_OR_PATH]

To add readable, writable and executable permissions to any file or directory:
chmod +rwx [FILE_NAME_OR_DIRECTORY_NAME_OR_PATH]

To add user permission:
chmod u+ [FILE_NAME_OR_DIRECTORY_NAME_OR_PATH]

To add group permission:
chmod g+ [FILE_NAME_OR_DIRECTORY_NAME_OR_PATH]

To add others permission:
chmod o+ [FILE_NAME_OR_DIRECTORY_NAME_OR_PATH]

To add user and group permissions:
chmod ug+ [FILE_NAME_OR_DIRECTORY_NAME_OR_PATH]

To add user and others permissions:
chmod uo+ [FILE_NAME_OR_DIRECTORY_NAME_OR_PATH]

To add group and others permissions:
chmod go+ [FILE_NAME_OR_DIRECTORY_NAME_OR_PATH]

To add user, group and others permissions:
chmod ugo+ [FILE_NAME_OR_DIRECTORY_NAME_OR_PATH]

To add user, group, and others permissions with [read or writable or executable permissions]:
chmod ugo+[read or writable or executable permissions] [FILE_NAME_OR_DIRECTORY_NAME_OR_PATH]

To remove:

To remove readable permission to any file or directory:
chmod -r [FILE_NAME_OR_DIRECTORY_NAME_OR_PATH]

To remove writable permission to any file or directory:
chmod -w [FILE_NAME_OR_DIRECTORY_NAME_OR_PATH]

To remove executable permission to any file or directory:
chmod -x [FILE_NAME_OR_DIRECTORY_NAME_OR_PATH]

To remove readable and writable permissions to any file or directory:
chmod -rw [FILE_NAME_OR_DIRECTORY_NAME_OR_PATH]

To remove readable and executable permissions to any file or directory:
chmod -rx [FILE_NAME_OR_DIRECTORY_NAME_OR_PATH]

To remove writable and executable permissions to any file or directory:
chmod -wx [FILE_NAME_OR_DIRECTORY_NAME_OR_PATH]

To remove readable, writable, and executable permissions to any file or directory:
chmod -rwx [FILE_NAME_OR_DIRECTORY_NAME_OR_PATH]

To remove user permission:
chmod u- [FILE_NAME_OR_DIRECTORY_NAME_OR_PATH]

To remove group permission:
chmod g- [FILE_NAME_OR_DIRECTORY_NAME_OR_PATH]

To remove others permission:
chmod o- [FILE_NAME_OR_DIRECTORY_NAME_OR_PATH]

To remove user and group permissions:
chmod ug- [FILE_NAME_OR_DIRECTORY_NAME_OR_PATH]

To remove user and others permissions:
chmod uo- [FILE_NAME_OR_DIRECTORY_NAME_OR_PATH]

To remove group and others permissions:
chmod go- [FILE_NAME_OR_DIRECTORY_NAME_OR_PATH]

To remove user, group and others permissions:
chmod ugo- [FILE_NAME_OR_DIRECTORY_NAME_OR_PATH]

To remove user, group and others permissions with [read or writable or executable permissions]:
chmod ugo-[read or writable or executable permissions] [FILE_NAME_OR_DIRECTORY_NAME_OR_PATH]


Another examples:
chmod [u and or g and or o]+ or -[r and or w and or x] [FILE_NAME_OR_DIRECTORY_NAME_OR_PATH]