Humans communicate not just verbally but also through non-verbal body language, gesture, signs etc. And anyone who has been to any foreign land will understand this fact that hand gestures play a huge role in communicating in a place where you have no means of understanding the local language or or making the locals understand what you want to say.
But sometimes, these very hand gestures can put you into trouble because if you do not know what is considered right and what is considered offensive among the locals, you might actually find your self in a false positions with them.
Which is why, it is recommended that you first learn the basic hand gestures that are acceptable or non-acceptable at a foreign land.