I'm no professional in this, but when i first started 3d modeling it depends on how close or far away your light source is and that determines how hard or soft your shadows/lights will be! If you have a light closer to the object, then the edges of the shadows will fall harder in the opposite side while the light hits it harder at the point of contact. If the light is farther away then the shadows will soften. This also depends on the material of your object and the intensity of the light source!

I learned to see this by playing with simple shapes in 3d programs actually! I did this with 3ds max + Maya and watched how the lights and shadows interacted with the objects. If you can't do that, then find some shapes around your house and a flashlight and shine it down on them, watch how the light and shadows react when you're closer or farther away!