Cryptocurrency and Blockchain ☺✌ 

This application is pretty interesting educational and fun to use. There is a similar app called cyber security which teaches you about another topic but in the same format as this. The first few sections are free but in order to complete the entire course and receive a certification you must upgrade to pro however I don't believe the costs are excessive. These courses give you an in-depth understanding but give it to you in small easy to understand pieces.