This is actually a great question, because it helps to illustrate a basic point of the *nix file structure.
"." referes to the current directory. This is important, for example, when you are compiling software. Very often there is a configure script to configure how the software should be built. You would enter the command './configure' from within the source directory of the new software, and the "." indicates to the OS that the particular configure script you want to use is in the current directory.
".." points to the directory directly above working directory you are in at the time. So, if you drop down into your bin directory to edit one of your scripts and then want to go back to the next directory higher, you can type the command 'cd ..' to go there.