Create new file with 750x750 and 72 dpi. Paint it with the color 4A4A4A

Use the instrument

to represent a square with the parameters below. Place it like in the picture.

Blending Options-Gradient Overlay

Gradient’s parameters

Use the same instrument

to create a white color square inside the previous one.

Take the same instrument and picture a square with the color 666666 inside the recently created one.

And one more with the same instrument and indicated parameters below

Blending Options-Inner Shadow

Blending Options-Gradient Overlay

Gradient’s parameters