Shutter Speed

Determines how long the camera's sensor is exposed to light. A fast shutter speed such as 1/1000s freezes the motion whilst a slow shutter speed like 1/10s allows motion blur and more light in - water is a good way to experiment with this. 

 

Aperture
Controls the amount of light entering the lens. A lower f-number like f2.8 allows more light in, creating a shallow depth of field (background blur), but a higher f-number like f16 lets in less light and increases depth of field (everything in focus).

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ISO
Controls the sensor's sensitivity to light. A lower ISO such as 100 produces cleaner images with less noise, but using a higher ISO such as 3200 will brighten your image but it will ultimately introduce grain and noise into your photographs.