Shutter speed is a measure of how long the camera sensor (or film, in analog cameras) is exposed to light. It is usually stated as a fraction of a second, like 1/125, 1/1600 or 1/2 second.
The longer the shutter is open, the more light gets to the sensor. Light is good since it gets out many details in photos. On the other hand, when the shutter is open longer, the risk of camera shake increases. Therefore we always have to balance shutter speed between getting as much light as we need and not getting blurry photos because of shaking.
Most people can hold a camera still down to a shutter speed of 1/60 second. Many trained photographers can manage down to 1/30 or 1/15 second. With a tripod, or other stand, camera shaking isn’t a problem. Use a camera stand in situations with low light.
Another problem, or challenge, with slow shutter speeds, is that moving objects can get blurry. This can be an advantage if you put the camera on a tripod and shoot a waterfall with a long exposure. Everything around the waterfall will be sharp and crisp but the moving water will look soft and dreamy.