These photos demonstrate what a catch light is. You see the light reflection in her eyes? That’s the catch light. It helps add to your photos when used properly. The good news is that it is difficult to screw up. The better news is that you have numerous ways to impact catch lights.
You can impact the size and shape of the light by changing the size and shape of your light. For example, if you use a large soft box the catch lights will be large. If you use a rectangular softbox the catch lights will be rectangle in shape. Or if you have an octagon softbox, they will be an octagon or circular in shape.
You can also change the angle of your light or the distance. Moving the light closer or further will change the size. Changing the angle will warp the shape of the catch light.
In all honesty, this is really something you want to play around with and practice to better understand and get a strong command of. Knowing something exists and knowing how to use that something are two different things. Being able to use catch lights can help you improve your photography and make better photos.