ISS is quite big. It’s by far the biggest structure, that orbits the earth and can be easily seen when it passes over and weather is clear.
ISS started as an international cooperation project to build laboratory, observatory and factory in space. Many modules have been added in the more than the fifteen year it orbits the earth. This cool animations shows how it all started in 1998 and how ISS did grow to it’s present state by adding and relocating modules.
You probably have to watch this video two or three times and pause it regularly, to get a grasp of all the information that’s in it.