What should I do if the photos taken by SLR are blurred?

Specific analysis of specific problems:

Set to manual focus.

Solution: this can be set to automatic plus manual focusing, with automatic focusing as the main and manual focusing as the auxiliary.

insufficient light

Solution: Take photos in a well-lit place and turn on the flash to supplement the light source.

Inaccurate focus

Solution: If the autofocus point is not what you want, you can adjust the focus yourself. If you take care of two people, you can concentrate on them.

The camera shakes when shooting.

Solution: Keep your hands balanced when taking pictures, if you can use a special bracket for taking pictures.

The solution to moving the subject: adjust the shutter speed.

1/400 seconds of running water photos are basically still and not blurred.

Equipment problem, camera setting problem

Solution: Replace camera equipment and modify camera settings.