In the examples below, "you" means whatever class of users the specified three permission bits refer to, which could be you as the owner of the file, you as a member of the group which owns the file, or you as anyone else not in the previous two categories.
rwx (octal 7) lets you do anything
r-x (octal 5) lets you read or execute a file, or list or search a directory
--x (octal 1) lets you execute (but not read) a file, or search a directory for a specified file, but not get a complete listing of directory contents
r-- (octal 4) lets you read a file, but not modify it
-w- (octal 2) lets you write into a file, but not read it
r--, -w-, rw- are pretty much useless for directories