Check "The folder metaphor" section at Wikipedia. It states: There is a difference between a directory, which is a file system concept, and the graphical user interface metaphor that is used to represent it (a folder). For example, Microsoft Windows uses the concept of special folders to help present the contents of the computer to the user in a fairly consistent way that frees the user from ...
Every directory on a Unix system (and probably every other system too) contains at least two directory entries. These are . (current directory) and .. (parent directory). In the case of the root directory, these point to the same place, but with any other directory, they are different. You can see this for yourself using the stat, pwd and cd commands (on Linux): $ cd / $ stat . .. bin sbin ...
directory - What are ./ and ../ directories? - Unix & Linux Stack Exchange
windows - What are "." and ".." in a directory? - Super User
In bash all I know is that rmdir directoryname will remove the directory but only if it's empty. Is there a way to force remove subdirectories?
~ expands to your home directory, as has been pointed out, but I think it's worth noting that isn't a feature of ssh itself. ssh (among many other wonderful features!) lets you establish a remote shell, and this shell can provided by many different pieces of software. On a *nix system, your account will be associated with a particular shell, GNU bash is a popular choice. And it so happens than ...