How do you protect your Bitcoin bank account from adding a duplicate transaction(s)

Read the article below and address the following questions regarding blockchain:

https://www.weforum.org/agenda/2017/11/blockchainbitcoinethereum-tech-explained/

1. What do you know about Blockchain?

2.  How do you protect your Bitcoin bank account from adding a duplicate transaction(s) i.e a $5,200.00 debit . ?