Now a days people are mostly talking about blockchain so it will be a broadly speaking topic in near future,blockchain is simply a peer to peer transactional system which you can transfer coins to someone directly without any involvement of third party.
so a blockchain platform would be like Microsoft Windows or MAC or Android. But the difference is it's built from ground up on blockchain technology and instead of being run from a single computer or a online server, it's run from many many computers (nodes) that make up the network now a dAPP is an APP that runs on a blockchain. They are specific to the blockhain they are written on so Microsoft Windows would be like EThereum or NEO or Zilliqa and say Microsoft Office would be like a dAPP built to run on etherereum.
there are so many terms to learn in a blockchain like sidechain,sharding,offchain scaling,consensus mechanisms etc.i think blockchain is a very vast technology that each and everyone has to learn something everyday.so let us discuss some of the above terms very simply.
sidechain is a another blockchain which reduces the workload of the main network Plasma is a sidechain that LINKS to the main Ethereum chain this means it is another separate blockchain that is attached to ethereum.because those dApps on Ethereum will send some of their transactions to the Plasma chain, which will handle those transactions. Then those transactions will be put back on the main Ethereum chain when done so Plasma 'offloads' the load from Ethereum because it takes on some of the work load.
Sharding is a different technology. It's basically a solution where the actual PLATFORM itself is speed up by modifying how the consensus works where all the nodes are grouped up into 'shards' and each shard works on processing a transaction as a mini blockchain of sorts with the results then tabulated and the final result agreed on.
Offchain Scaling is also called State Channels. For Ethereum, this would be the Raiden Network. For Bitcoin, this is called The Lighting Network this idea is simply to take a transaction, record it on the blockchain, but then send the computations to a server that's NOT on the blockchain to process. When it's done, send the answer/result back to the blockchain to lock it in.
you could also look at doing offchain stuff like lighting but the bottom line is each of these technologies are still being worked on individually and not yet close to prime time (or in some cases, not even developed outside of a whitepaper.
consensus mechanism is a fault-tolerant mechanism that is used in computer and blockchain systems to achieve the necessary agreement on a single data value or a single state of the network among distributed processes or multi-agent systems. It is useful in record-keeping, among other things.
public blockchains that operate as decentralized, self-regulating systems work on a global scale without any single authority. They involve contributions from hundreds of thousands of participants who work on verification and authentication of transactions occurring on the blockchain, and on the block mining activities.
In such a dynamically changing status of the blockchain, these publicly shared ledgers need an efficient, fair, real-time, functional, reliable, and secure mechanism to ensure that all the transactions occurring on the network are genuine and all participants agree on a consensus on the status of the ledger. This all important task is performed by the consensus mechanism, which is a set of rules that decides on the contributions by the various participants of the blockchain.
There are different kinds of consensus mechanism algorithms which work on different principles such as proof of work(pow),proof of stake(pos),proof of capacity etc.will discuss those thing later in a different article.
so i hope you may have some idea about blockchain don't worry if you understand those terms u will learn it one day because i am also still a newbie to this world
Thank you