What exactly can you do with various permissions?
r -- list the directory, and only list it. Without +r, you can't list it, but you can do stuff if you know the filename (or make a new file)
x -- directory traversal. With this, you can do things to things inside of the directory, depending on what you have permissions for. Without +x, you can't change or access the directory's contents.
w -- needed to delete files in the directory. If you have +w permission on the directory, you can delete any file in that dir, even if you don't have +w access to the file in it. You can write to/touch new files in the dir., and
t -- from the chmod man page, if this is set on a directory (like tmp), you can't mess with files that belong to someone else, counteracting some of the bad parts of +w above.
g+s -- when new files are created, they inheret the group ID from the directory.
Only the owner can change the mode/ownership/group of a file