People are always blurred when taking pictures with SLR Nikon d90.

I'm a D90 myself. I have used it for a long time. According to my experience, I will rule out the lens problem first. The first thing to consider is that you have chosen the wrong point. First of all, you should unlock the focus (there is an L at the lower right, which means locking, and then you can unlock it by moving to another position), and then you can select the focus by rotating the pulsator. If you moved the focus before and then locked it, you can focus no matter what you do later. The main focus is no longer where you want to shoot, it must be blurred. In addition, you should turn on the smart 3D focusing mode, so that the focus will automatically focus with your lens, and you can focus normally!