A strange problem with arduino LED

hello genius
I hope you have a good day
yesterday I try to program some push button but I see the LED is on when I make my hand close to the arduino but when I make my hand far from arduino the LED is off automatically and when I close slowly I see the LED is flashing
see the video I hope you found some things

You omitted to set pinMode(yourbuttonpin, INPUT_PULLUP) and connect the button from yourbuttonpin to ground.

There seems to be a rule that when ever anyone says something is strange it is in fact perfectly normal. See this to see where you are misunderstanding things:-
http://www.thebox.myzen.co.uk/Tutorial/Inputs.html