Let’s say I press the left button at the beginning of the game and the player moves back and it got to the edge of the game beginning and the player falls down.
How can I do it that the player won’t be able to go to the edge of the game beginning even when the left button is pressed (though the left button is working) and how can I achieve it without putting a block at the beginning of game.
Why don’t you want to put a block? 
you can make it invisible.
Otherwise, you can use the player’s X position as condition.
Okay.
Thank you.
I will try that