Like many ingredients touted as beneficial in skincare products, you can add activated charcoal to the list of "newest fads."
Charcoal is the result of burning a carbon rich material (like wood) at a low heat without oxygen. It creates a non-porous (without spaces) carbon substance. Heat up this substance with steam (oxygen) in a pressurized environment and activated charcoal is the result. Unlike charcoal, activated charcoal is porous, filled with many tiny sponge-like spaces or pores. All these little spaces within activated charcoal create a large surface area that is particulary helpful for "soaking up substances."
Although there is little, if any, scientific evidence proving efficacy, manufacturers often claim that activated charcoal in skincare products can absorb oil from skin pores, draw out dirt that other cleansers cannot reach (which probably means you're using the wrong cleanser), and remove "toxins" (although manufacturers never identify exactly which "toxins" they're talking about.) Some manufacturers go so far as to claim that activated charcoal has anti-aging properties.
After review of the dermatologic literature, no clinically significant scientific evidence proving the claimed benefits of topically applied activated charcoal in skincare products could be found. Products containing activated charcoal are usually inexpensive, and due to their black color, pretty cool looking. So although no scientific evidence proving any benefits of topically applied activated charcoal could be found, there was no evidence finding it harmful, either.
The best skincare advice: Moisturize, apply daily sunscreen, live a healthy lifestyle (eat a healthy diet, get adequate sleep, exercise regularly), and if you have a little disposable income and wish to "have fun" with a trendy, neat looking skincare product that contains activated charcoal, go for it!