Make a pushbutton uicontrol (or menu item) and give it a callback that creates a new figure window. This figure has a static text box uicontrol and a pushbutton that closes the window.
A nice trick is to give the figure a unique tag. Then your callback can do a findobj on that tag first. If it finds anything, it just makes the figure current. If not, then it creates it. That way you won't create new help windows every time you click on "help".
You can also give mouse hover/tooltip strings to you uicontrols.