Question - Quora
If you are a complete beginner, I would suggest starting off with Bitcoin. Try to understand what Bitcoin is and how it works then you can dive in into more complex topics. This is one of my favourite videos on the subject:
While reading about blockchain as a technology, you will probably encounter many technology related terms like blocks, mining, Proof of Work (PoW), Proof of Stake(PoS), smart contracts, hashing, etc. You will need a Glossary.
As a next step, I would suggest creating a wallet and playing with the software sending transactions back and forth. This way you get to interact with the Bitcoin blockchain. Start off with $10 USD you don't need to buy a whole Bitcoin. You will learn about addresses, backups and private keys. A great wallet for beginners is Copay. Here is a tutorial on how you could buy Bitcoin: Cryptocurrency Tutorial
A community generated FAQ on Reddit could help you with many questions you may have: Bitcoin FAQ
An excellent source of information is the Bitcoin whitepaper published in 2008 by Satoshi Nakamoto. Read the paper couple of times and try to understand it. This is where all started. Here is another link explaining the blockchain technology: Blockchain Intro.
If you are a developer or have a technical understanding of the blockchain, you can watch the video by Andreas M. Antonopoulos about the Bitcoin blockchain, consensus rules, hashing, etc.
Developers should also check out the Bitcoin repository on Github.
There are different types of blockchains: public(Bitcoin is a public blockchain), private, consortium blockchains and hybrid blockchains. Read more at Blockchainhub.
If you prefer reading a book, I would suggest reading Mastering Bitcoin by Andreas M. Antonopoulos. IMO the book is a great read if you already have some previous knowledge(you can skip the technical parts of the book and still understand the technology). A new issue of the book is coming out soon. Follow Andreas on twitter for updates.
After getting an understanding about Bitcoin, you could start exploring other blockchains like Ethereum, Zcash, Dash, Monero etc. Find a list of all publicly listed blockchains here and read the whitepapers on their websites. Join their communities on Reddit or Slack, read the news and with the time you will get the big picture.