This lesson adds another millis() timer and 'if' statement with the same structure as lesson 12. Now the loop will execute as quickly as possible, executing one 'if' every 300 milliseconds and another 'if' every 600 milliseconds. Don't allow the number of lines of code to overwhelm you- think about the different parts of the loop and how they fit together like blocks.
This lesson creates a visual effect, but doesn't impact the way the game is played very much. Adding these types of features is up to you as a programmer. Sometimes, you may want something that 'just works', even if it is not pretty. Other times, the way the product looks to you or your user may be much more important than how smart the code is.
In either case, we encourage you to write well-structured code. That way, even a simple program is easier to enhance in the future.