However, these beta versions may still contain errors. Only after an update has been deployed successfully, i.e. without any error reports, to the beta channel it will be made available on the main / default channel to all the other users. Usually, when there is an error in a beta version the relevant update follows within one or two days. So, the frequency of updates to fix any errors and add new features is much higher on the beta channel.
To join the beta channel open the Google Play Store app on your device and search for the app you would like to become a beta tester for (Avia Weather or Avia Maps). When you are on the detail page for the app make sure that you have it installed and scroll down. There will be a section labeled "Join the beta". Touch the "Join" button, and welcome to the beta channel!
Be advised, that the Beta channel does not differ in licensing matters.