How does AF Point work?

What is AF Point? AF Point is the point you focused, or you want to be focused. You can see the AF
Point in the Viewfinder. 

In Auto Mode including Portrait Mode, Landscape Mode and etc, AF Point is actually fully selected, or I should say the camera will try to focus the nearest distance at any AF Point of the camera most of the time. Therefore, the selection of the AF Point looks like this. 

When the AF Point is fully selected, it is quite annoying because you will see the Red Square keeps blinking on somewhere you do not want to focus. If there is a lot of things at the subject's background, the camera might focus on the background instead of the subject.  

In Manual Mode including Shutter-Priority Mode, Aperture-Priority Mode and etc, the AF Point is selectable. You can select one of these points as your desire AF Point by pressing the AF Button.

Some digital camera might not exactly looks like this, but you can look for a symbol which is dotted cross within a white box. Then, you can select your desire AF Point and you will see something like this. 

However, You are allowed to select any ONE of these points OR FULLY select the AF Point, but you  are NOT allowed to select the AF Point in this way.

Do you want to know more? Please correct me if there is any mistake ^^

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