File Permissions

Files have 3 permission categories. User, Group & Everybody.
Files require the execute permission in order to be executed.
Directories have the same permissions.
Directories require the execute permission in order to create files inside them.

1=execute
2=write
4=read
you can add them together to combine their affects.

ls -l - shows files with their permissions
chmod 400 - (-r--------) User(Read),Group(None),Everyone(None)
chmod 600 - (-rw-------) User(Read + Write),Group(None),Everyone(None)
chmod 640 - (-rw-r-----) User(Read + Write),Group(Read),Everyone(None)
chmod 660 - (-rw-rw----) User(Read + Write),Group(Read + Write),Everyone(None)
chmod 666 - (-rw-rw-rw-) User(Read + Write),Group(Read + Write),Everyone(Read + Write)
chmod 700 - (-rwx------) User(Read + Write + Execute),Group(None),Everyone(None)
chmod +x - this will add the execute permission to the User category.
chmod g+x - this will add the execute permission to the Group category.
chmod -x - this will remove the execute permission from the User category.