Design has functions. There are designers working on lamps and coffee cups and chairs and computer keyboards. They keep in mind how these items will be used — their function. You are going to create your own country and design money and a flag.
MONEY: What’s the key consideration in designing paper money in the modern world? Worries about counterfeiting! So you must make a complex design with patterns and the look of textures. And yet at the same time it has to be easy to see the national identity and the denomination (amount). Do NOT make your money look like American dollars. Design front and back of paper bill. (save as a JPG)
FLAG: Most flags will be made out of cloth. Perhaps a version of the flag will be cut out of metal. Therefore the design has to be made up of clean geometric shapes. And yet the colors and the shapes must represent something about your (imaginary) nation. Also, based on the colors, symbols and shapes, we need to know that the flag and the money are from the same country. (save as a GIF)