Read the help file? Startup to get information that R goes through the start-up process and how you can automate the code that is executed.
I did things for clients where I create a GUI for a specific demo (I use tcltk, but everything should work the same way). I created a desktop shortcut for them and changed the shortcut for launching in a specific folder (but I launched the standard Rgui program), and then in this folder I saved a .Rdata file with all the code and data that the demo and the named function need. The demonstration starts first.
Then the client does not need to know anything about R, just double-click the shortcut and R will start and my demo will start automatically for them, they enter some numbers, select some parameters, shift some sliders, etc. and click on "OK" to see a graph or other result configured for their situation.
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