Need Help! what's the difference between servo motor and stepper motor ?

I would like to get a protable cnc router for engraving metal woman decoration. the material maybe copper,aluminmum or jade.The size is within 300*300mm
i have inquired some suppliers,they give me some advice, but right now i don't i should choice servo motor or stepper motor ?

Is there anybody can tell me what's the difference between servo motor and stepper motor ? :stickpoke