This is a hands-on lab from a Youtube channel "Coding in Flow" which demos how to write a simple countdown timer.
Coding in Flow Channel: https://www.youtube.com/watch?v=MDuGwI6P-X8&list=PLrnPJCHvNZuB8wxqXCwKw2_NkyEmFwcSd
Code In Flow Website: https://codinginflow.com/