Computer programming is a way to solve problems. People pay you money to solve their problems.
You need to make the connection between some code you wrote and a potential problem that could be solved with that. It doesn't have to be too fancy or complex, but this connection will be clearer to your dad than showing him a game or library method. Examples:
- A simple web application. Work through a tutorial of a programming book, and it will show how to make a web-app for a pretend store.
- Make a simple calculator program
- Make an address book program that keeps your contacts
- Make a calendar program
- Make a mathMath equation program. I don't know what level of Math you are on, but one of the first programs I worked onmade was for finding the hypotenuse of a triangle.
After you do something like that (or simpler), you can show that you can customize these programs yourself with your programming knowledge.