Shutter Speed is one of the three pillars of photography, also known as the Exposure Triangle. The other two are Aperture and ISO.
It is defined as the length of time that the camera shutter is open to expose light into the camera sensor. Measured in seconds, the Shutter Speed controls two aspects — motion and exposure.
Motion is created by making the Shutter Speed fast or slow;
Using a faster shutter speed freeze frames any motion.
Using a slower shutter speed exaggerates motion blur, where moving objects appear blurred along the direction of motion.
The brightness or darkness of the image (exposure) can be controlled by adjusting the shutter speed.
A faster shutter speed results in a darker image, because less light hits the camera's sensor in such a short duration.
A slow shutter speed results in a brighter image, because more light hits the camera's sensor over a longer a longer period of time.
I hope this rundown on Shutter Speed will help you with get more creative with your photography.