IDLE is the Python Intergrated Development Enviroment (IDE) which is basicly a tool that has all of a particular programming language's tools in one area. It's a powerful code formatter to make code better orginized durring writing, and it also can make calls to the Python compiler. It just takes everything you can do with the Python langauage and puts it all in one place. It's just adds a General User Interface (or GUI) on top of the Python commnand line.
A GUI is anything that isn't command based (aka the Windows Prompt, Bash, Midnight Commander, etc...). For Python there are serveral GUI Toolkits (librairies that you can use to build GUIs instead of just console applications). The standard GUI toolkit that comes with Python is Tkinter (based off of TCL and Tk), but a lot of people find the code cumbersome. There are also wrappers for GTK, OpenGL, wxWindows, qt, pygame, and a few other you might find when looking around.
Hope this answeres your questions
