When enabling the Avast Firewall, you get this message:
Could not acquire root access. You needs a rooted phone to run the avast! firewall.
If this phone is already rooted, please make sure the avast! firewall has enough permissions to execute the SU command.
Basically, as the Avast Firewall states:
This feature requires root access as it is not possible to realize meaningful firewall features without root access.
To understand this, you need to know what Phone Rooting is. Routing your phone is basically modifying the Android installation so that you can gain root (Administrative) access to the mobile phone. Rooting your phone will invalidate your warranty, so you may want to think twice about enabling the Avast Firewall.
Phone Rooting is different on each phone, so to find out how to root your phone, search the internet for the following:
«Mobile Phone Model» root xda
You can use the search box at the bottom of this article to search in Google, just remove the Could Not Acquire Root Access – Avast Firewall text.