Google is your friend.
https://www.investopedia.com/terms/b/blockchain.asp
https://en.m.wikipedia.org/wiki/Blockchain
https://www.euromoney.com/learning/blockchain-explained/what-is-blockchain
https://builtin.com/blockchain
https://www.edx.org/learn/blockchain
https://www.coursera.org/learn/blockchain-basics
https://www.blockchain-council.org/blockchain/how-can-a-newbie-start-learning-about-blockchain/
https://www.coursereport.com/blog/getting-started-blockchain-bootcamps