1. If you are the owner of a directory, owner should have readable and executable permission for the directory to cd into it or list the content of the directory.
If you are not the owner of a directory, other users should have readable and executable permission for the directory to cd into it or list the content of the directory.
2. If you are the owner of a directory and owner has only readable permission for the directory, owner can list the files and sub-directories inside directory but owner cannot read the content of the files or list the content inside sub-directories. Owner cannot cd into the directory.
If you are not the owner of a directory and other user has only readable permission for the directory, other users can list the files and sub-directories inside directory but owner cannot read the content of the files or list the content inside sub-directories. Other users cannot cd into the directory.
3. If you are the owner of a directory and owner has only executable permission for the directory, owner cannot list the files and sub-directories inside directory but owner can read the content of the files if owner knows the file name. Owner can cd into the directory.
If you are not the owner of a directory and other user has only executable permission for the directory, other user cannot list the files and sub-directories inside directory but other user can read the content of the files if other user knows the file name. Other user can cd into the directory.
4. Complete directory structure of files and sub-directories follows above rules.
If any of the sub directories has missed the correct readable and executable permissions, the files and sub-directories of the directory cannot be listed or read based on the given permissions to parent directory.
If a sub-directory or a file has full permission but parent directory does not have readable or executable or both permissions then sub-directory content or files cannot be listed or read based on the given permissions to parent directory.
