Every EOS digital camera has multiple AF Points, from 9 in the EOS 1100D to the 61 in the EOS-1D X and 5D Mark III cameras.
With automatic AF Point selection, subject distance readings are taken by each of the points when you press the shutter button. If more than one point lights up it means that that these points are supplying similar focusing distances to the camera.
Each focus point is capable of passing accurate focusing data to the lens, so why are there so many? It is so that you can select the point or points you want to be active. This is done by pressing the button in the top right of the camera back. Then turn the Main Dial select one, some or all the points.
An active AF Point lights up in red in the camera viewfinder and takes a distance reading from the nearest part of the subject to the camera. Inactive points do not take readings.
Usually it makes sense to choose the centre point as this is the most sensitive. Position this point over the area of the subject you want to be in focus and then partially depress the shutter button. This will lock the focus. Now you can recompose the image in the viewfinder and fully depress the shutter button to take a picture. Alternatively, you can choose an off-centre focus point to be active. Choose a point that covers the area of the subject you want to be in focus.