Basic overview:
https://www.youtube.com/watch?v=SSo_EIwHSd4More detailed demo/example:
https://anders.com/blockchain/Honestly a lot of companies dont need a blockchain, and a lot are repackaging "blockchain solutions" as a way of selling well basically a database. There is some use cases for blockchains, but a lot of companies wont ever need one. Immutability can be achieved by using hashes in a database, no need for using a cumbersome blockchain for that purpose. Decentralization is useful to prevent censorship, but does a company need that for what is effectively a database/ledger. No in 99.99% of cases.
You will hear about projects, ICOs etc all claiming to launch a blockchain to be the next big thing for a particular sector of finance, industry, logistics, shipping, housing etc etc. Very few actually need a blockchain, let alone there own token.
Bitcoin uses a blockchain and as such is the best example of something that requires a blockchain for decentralization and immutability.
Look into bitcoin, the satoshi white paper and that will help give you an understanding of the bitcoin blockchain.
From a programming point of view, contributing to a open source cryptocurrency, or creating a tool/utility that helps users interact with blockchains (bitcoin etc) like full node software wallets, spv wallets, or block explorers are where the majority of development is, as far as i know. Other programming that is useful to look into is with the lightning network with 3 implementations so far (all open source) and the zap wallet for the lighting network.
