ISO is the sensitivity of your sensor to light. The higher the setting, the more sensitive the sensor gets, but also the higher the noise. It's kind of like turning up the volume knob on a radio. Lower ISOs are good if you can use a slow shutter speed and you want to minimize the noise. Higher ISOs are good if you need a faster shutter speed (say, to freeze subject motion or minimize camera shake blur) and you're willing to live with the noise.
Aperture is how wide the lens opening is. It's given with an f-number, and the smaller the f-number, the larger the opening is. The larger the opening, the more light gets in, but the smaller your DoF (i.e., the less stuff you can hold in focus) becomes. A large aperture (say f/2.8 to f/1.4) is useful if you're in a low light situation and you want to use a faster shutter speed, or you want to throw the background out of focus to concentrate attention on your subject. A smaller aperture (say f/8 to f/16) is useful if you don't want to misfocus or you want everything to be in focus, like say for landscape photography.
Be aware that the aperture range you can use depends on the lens you're using. That's why a lens is described with both its focal length and its maximum aperture.
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