First, component-scan element configures Spring to scan all classes under specified package and autodiscover beans. That's how it's able to find your DAO.
You don't need a <bean> tag for the service bean either; it too will be autodiscovered.
Read about component scanning
here.
Second, default behaviour of autowiring is to match by type. Your setTrackingDao setter method tells Spring to use setter based dependency injection. It checks the type of the member, sees that it's a TrackingDao, finds the TrackingDao class as part of component scanning, creates an instance of it, and injects it into your service bean.
Read about setter based DI
here.
Important: From now on, when posting in CodeRanch, ensure that you enclose all code snippets in your question inside Code Tags for improved readability. See
https://coderanch.com/t/659781/Wiki/Code-Tags for instructions. I'll edit your post and do it for you this time.