Shutter speed, and the second thing it does
12 min
Shutter speed is usually taught as the brightness control. It is, and that is the half that causes the trouble, because the blurry photo you cannot explain is the other half.
Shutter speed is how long the sensor is allowed to collect light. It does two jobs at once, and people learn the first one and get caught by the second: it decides how bright the picture is, AND it decides whether movement comes out sharp or smeared.
How you set it depends on what you hold. On a camera with a mode dial, it is the S or Tv position. On a phone, it is inside a manual or pro mode if your phone has one, and if it does not, you steer the shutter speed by controlling how much light reaches the phone, which works better than people expect.
Go and do this
Photograph the same moving thing twice, once as bright as you can get it and once in the dimmest light you can find indoors. Do not change anything else. Look at which one is sharp and work out why.
Bring a photograph back for this