To execute ruby, you need a ruby interpreter. If the machine you want the program to run on doesn't have a ruby interpreter, then you have to package up a ruby interpreter with your code.
With full service languages like ruby (v. php), you create gui applications, i.e. applications that open up windows with text boxes, buttons, etc., with one of the gui packages available for that language. Ruby, like other languages, has a variety of gui packages available including tk, wxruby, and shoes. However gui programming is an intermediate to advanced topic, so you will need a good grasp of a programming language before embarking on such a project. In ruby, shoes is kind of beginner level gui package with limited features, so you might want to take a look at that first.
ruby is a pretty crazy language that at a certain point becomes write only.