Topics to learn

1. Solidity version
2. contract keyword
3. Variables
4. Data types
5. If elses
6. Loops
7. require
8. Functions
   1. Arguments
   2. Return types
9. Function visibility
   1. external
10. Mappings, Arrays
11. structs
12. Modifiers
13. Custom Modifiers
14. memory
15. Returning tuples
16. pure functions
17. memory vs
18. Events
19. Inheritance
20. External contracts, Ownable
21. CPIs