Making your own blockchain app | Part I : Introduction to blockchain

A blockchain is a continuously growing list of records, called blocks, which are linked and secured using cryptography and each block typically contains a hash pointer as a link to a previous block, a timestamp and transaction data.

As you can see on picture how each blocks inherits signature from preceding block.

About the first block(Block X in the above picture):

It's called 'genesis' block.
-Every block is connected with next block but it all started from 'genesis' block.
-It is configured in genesis.json file, a config file.

Creation of new block:
How is new block actually created? Here is the brief information about it:

Blocks needs to mined. It is mined by miners.
How do they do it?
-Solving a mathematical riddle which is hard to find the answer but easy to verify.
For example: 3+x=8;find x? This a simple example just find the answer and replace the value and if it's correct it will get verified.

Bitcoin or Ethernum main network runs on Proof of Work as shown above in example which need more powerful devices and energy to solve riddles and mine a new block.

Creation of transactions:
How is a transaction created?

If you want send a data/value or amount of cryptocurrency to the network, you need to sign it with private key; these two together creates valid transactions and they are sent to the network and when the next block is mined the transaction will be included in the network.

Now the questions arises, what are private keys and public keys?
Private keys are the cryptographic hashes created in your computer. You should keep your private key.
Public key is derived from private key and is used to verify transactions. If you loose your private key, public key can't recover your private key.

About address:
Addresses are identifiers which you use to send cryptocurrency to another person. Addresses are derived from public keys.

Location of Blockchain:
Blockchain is massive distributed database and is saved in every computer. It's trusted if you(only you) hold the private keys. It is accessible through cliens and has various implementations such as for Ethernum there are GoEthernum(written in C++ and Go, open source project), Ethernum ++, etc.
The blockchain database system is not installed in server-side, it is accesible through the localhost.

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