The main purpose of using VPN (Virtual Private Network) is to hide your online activity from every one, that’s including your ISP (Internet Service Provider). Though your internet connection is encrypted, you have have doubt on “Will ISP know I’m using a VPN”.
The answer is YES.
Your ISP can still know that you’re connected to a VPN server, know your VPN IP server and amount of traffic being passed from/to you. But they cannot see the actual data traffic because it is encrypted. Means, they will not know what site you visit and what you do.
If you are using VPN from NordVPN, it has double encryption features. With this feature, you ISP will not know your final VPN IP address.
So when your ISP cannot see the actual data traffic, your online activity and browsing history will be saved.