Your isp whether is cable or cellular or satellite
Provides your base/trunk connection to the internet
And they route the connection to the internet back bone that takes you to the web pages you visit
It is Now legal for them to track this data and sell it, where and what you visit on the web and when you do it
A VPN encrypts this at the computer the only request thing your isp will know is that you are going to the VPN site , but not what web sites you actually go to or the content
Everything coming and going thru your isp between you and the VPN it's encrypted
They are the middleman , keeping your isp from seeing what data you are using
This way your isp does not know what Google searches you made, what videos you watched on YouTube, what movies you stream, or how often you visit Amazon, Wal-Mart, or eBay
I started researching isp last week
And i thank the OP for the information