Blockchains can be easily explained with a simple analogous of a kitty party. A kitty party includes a group of people who come together and create a pool of funds with manageable monthly installments. One winner is chosen at random from everyone who gets the entire amount for that month. Essentially, depending on when your name is picked, you get access to a lump sum amount by depositing small amounts of cash. Now, this system is highly transparent, and each participant in the network knows who has already received the money, who is yet to win, who all are regularly paying, etc. If anyone decides to fraud the system, they will have to convince at least 51% of the people, if not all. Blockchains are very similar in nature. They are distributed public ledgers where participants validate the transactions, and no single authority can make changes at will.