With follow-up mode, you can ask Alexa for further information or to perform additional actions after your first request. So, when you say something like "Alexa, show me comedy movies" and it shows a selection of such movies on your TV, you can ask to play a particular girl without having to say "Alexa" again. You can also use follow-up mode to request additional weather or item information on a list. You must enable the feature from the Alexa app settings if you want to use it.
Multiroom audio is again quite self explanatory ̵