"Camera shutter" is a curtain in front of the camera sensor. This curtain is closed until someone fires the camera with pushing the button that is called "shutter" or "shutter button". The length of time that this curtain remains open and the camera sensor is exposed to light, it is called "shutter speed".
If shutter speed is fast, that is above than 1/500 second for general photography, and above 1/1000 second for bird photography, motion is freezing completely.
If shutter speed is slow, an effect is formed, called "motion blur". In that case you can show motion in photos, like cars moving, or sports, in general something is shown moving.
In the photo you can see the difference, when a photo is taken in slow shutter speed, and when it is taken in a fast shutter speed.