Please read the Learning Centre: Experimenting with ISO
You may need to read your camera user manual regarding settings and how to change them.
Go out and take two photos, by setting your camera to mode (as per the first challenge), and selecting a suitable of your choice. Once selected, do not change your .
Take your first photo at 100
Take your second photo at 1600 (or the closest to 1600 your camera will allow)
Present both photos here and tell us what the differences are. Also consider what your camera did differently to get a correct , between the two photos.