Giving a box a shadow

Like this one has: http://www.chillskatemag.com/

It’s probably the most simplest thing in the world, and yet I can’t figure it out and can’t find any sort of tutorial related to it.

Something tells me I have to draw with the paintbrush, but when I do the brush isn’t soft enough.

Anyone care to help a lil stupid n00b? :h: :love: