Should i use one or more "Directional Lights" in my scene?

The problem is if i just use 1x light source in my scene i have much dark corners on my models and the shadows are just black and very intensiv. If i use multiple lights with different rotations it looks ok but the light is very bright and looks unrealistic. Thank your for ur help, im new to Unity ^^

You are missing ambient lighting from the environment (which used to be enabled by default, but isn’t). Go into the lighting settings and enable auto-generate at the bottom or bake the lighting yourself.