It's a wooden box which is played as a drum. Since it's early beginnings the design of the the cajon has not changed all that much.From the most modern up to date cajons with built in amplification and adjustable snare and bass tones to the most humble box, the cajon is still a hollow box usually made from plywood.
The cajon has a thin layer of plywood on one side....like the bottom of a drawer.....and thicker wood to the sides and top, usually the back of the cajon has a sound hole, and simply beating on different parts of the front surface will give different sounds.
A bass drum sound can be achieved from hitting the middle of the playing surface and higher toned sound can be achieved by hitting the box closer to the top. Thus one can play the cajon box drum in a similar way as one would a bass drum and snare or toms. This makes the box cajon a very versatile and easily transportable instrument.