Create a new windows forms application in C#, add a richtextbox to your form and a mainmenu, fit in some menu items like: File->New; File->Open; File->Save; File->Exit. Then you will need a fileSaveDialog and a FileOpenDialog. Put code behind the menu items open and save to call these dialogs the open or save the file made in the richtextbox. It shouldn't be that hard to make

I will post a sample for you.