Imagine a chess game. There are two players and the umpire. Each player, and the umpire writes down each move using chess notation. All three players have exactly the same moves listed. Their little books for chess notation will all say exactly the same thing.
Suddenly, the lights go out. When the lights come back on, some of the chess pieces on the board appear to have moved.
Each player can playback the entire chess game from the beginning, right up to the last move. Provided they kept accurate movements of each move, all three can agree on what the state of the board should be. There can’t be any dispute as to where the chess pieces should be.
In the event that one of, the arbitrator, or either of the two players disagrees about a particlar move, then the majority can overrule him. That’s how the blockchain works.
Those three books of notation represent the blockchain. They are three ledgers all saying the same thing. The blockchain is made up of tens, hundred or thousands of computers all saying the same thing.
The chess board represents the currentstate of play (or wallet balance).
Now imagine the game gets to a really interesting position,where there is more than one way to play. Some of the observers want to play in one way, which is different from the current players. The referee stops the game, and allows the observers to take a photocopy of the chess notation up until that point. The observers return to the other-side of the room and play gets readyto resume from the same position.
That was the hard fork. Now there are 6 sets of notation and they all say the same thing, at least up unil a certain point. From then on, the two games procced in a different way. We now have two chains, identical in every respect up until the moment of creating a new board, after which the games went in separate directions.