How can I set the SLR to shoot the smear effect? (for example, car lights drag shadows, flashlights write, etc. )

2, you can use shutter priority, you can also use M file.

3. Be sure to use a tripod when shooting.

4. The camera had better have a T-door or a B-door. The following is the effect of exposing the starry sky with T-door for several hours. The trajectory dragged by starlight is the result of the earth's rotation. You should know which star is at the center of the circle.