A CDC example for how contact tracing is important.
This short CDC video gives you a good example of how contact tracing can be important in stopping the transmission of COVID-19 in a community. It is only 2:36 minutes long, How COVID-19 Can Spread in a Community.
Testing and contact tracing are the answers to identifying people who have been exposed to the virus and then having them go into quarantine for 14 days. This is what will stop the spread.