I've never worked electronics or electrical engineering for that matter but have always been curious how an enlarged lego block with metal spikes can hold graphics; produce sound.
What's inside the casing of one, I know its something to do with transistors but what are those and what's inside them.
All cool, none the less.
Red, Green, Blue, Sync
And you need to deliver them at a steady pixel clock rate. Horizontal sync is between each scanline, and Vertical sync is between each frame. There are official standards to follow here, with things defined such as voltage ranges for RGB, voltage levels for Sync, "Front Porch" and "Back Porch" (how much blank space you have before and after Sync), horizontal frequency, vertical frequency (refresh rate), etc, etc.
Look for a video on Youtube called "The world's worst video card" for an example of constructing such a circuit.
https://www.nand2tetris.org/course
If you want more detail about how transistors and logic gates work, the Art of Electronics is pretty definitive.
Well explained and the parts used are not unobtainium, so one can follown along at home with real hardware, if one so desires.