Unfotunately, it was also designed in laboratory environments where security was not a big issue. We are constantly monitoring our machines for any security violation, but all users are asked to help by watching out for their own files. Unix associates permissions with every directory and file on the computer. The owner of the file refers to you. Group refers to the group that you belong to.
World refers to everyone else.
If someone has permission to read your file or directory, they can see what's in it. If someone has write permission on your file, they can modify its contents. If someone has execute permissions on your file, they can execute it. If they have execute allowed on a directory, they are allowed to go into that directory. The lines of the listing beginning with d designate that as a directory file.