Okay, sometimes the red dot appears sometimes it does not. I set it to center but then may have moved the point to another spot, i.e., focus on tip of nose half click; move to sunglass frame and then release shutter.
This will cause the focus to be out of wack, right?
Its not instantaneous, it will search for focus sometimes.
Well if theyre the same distance from the lens then no the focus wont get ruined, however if you're trying to take a picture of the sunglasses, and you focus on the tree behind the subject, then yes things will be blurred.
Listen, I'm not going to sugar coat it, GO PLAY WITH THE CAMERA, It will all come to you I promise. Things like aperture which aren't easy to get your head around, might come more difficult... but stuff like how the camera functions will all be picked up if you play with it enough. Nobody masters the camera without spending a considerable amount of time just fiddling.