I thought the VPN is a sort of external protection thing and didn’t realize it’s a browser as well.
A VPN service is not a “browser” itself.
It only hides you real IP Address, which is useful and can protect you while connected on public WiFi. And allows you access some country restricted websites (such as Netflix, Hulu and others).
Of course… it protects you while using your own internet as well.
VPN is useful in many cases and you have look for your own “utility” for using this service. 
I see. But must I use the Avast VPN “browser” to use surf the net? Right? I shouldn’t browse outside of its browser or it’s not protected?
Just connect to a server you want, open your prefered browser (such as Microsoft Edge, Google Chrome, Opera, Mozilla…) and start using your Avast Secureline VPN.
You have two choices:
- You can download TOR. It will change your IP address, and also encrypt your connection
(like when you go to your bank online, and you see that LOCK symbol on the address bar, which means NO ONE can see what you’re doing).
TOR is free and isn’t controlled by any government or corporation so you truly get privacy, BUT - you have to use the TOR browser.
2)OR you can buy VPN from Avast. It costs about $36 per year currently. BUT YOU GET TO USE YOUR OWN BROWSER.