DSLR Autofocus explained

ZY productions has created a great video explaining the various types of phase detection sensors that exist in a DSLR.  This will not apply for mirrorless cameras, only cameras such as DSLR's with their own separate phase detection sensor.

It really depends on the model of DSLR you have to what type of auto focus sensor and sensor points you have available to you, however, this video helps go beyond the bizzare sounding terms like "dual cross type" and gives you a good understanding on what you have, how to use them to your advantage, and how to make up for any (if any) short comings that you may experience while using AF.