Being human, one of the natural urges that we have is to communicate our thoughts and ideas to the people around us, be it verbally or non verbally.
But there are times, when language do not suffice specifically when the people we want to communicate our thoughts to, do not understand the tongue we speak in. Which is when body language comes into use, and that can be done through gestures or through postures or facial expressions.
But where there are certain universal gesture that mean the same thing every where, there are some that might actually mean something offensive in another place. For example where in Australia, UK, USA and Canada, the crossed fingers mean wishing someone luck, in Vietnam , it symbolizes the female genetalia and is considered extemely lewd.