Your internet service provider (ISP) will provide you with their Domain Name Server (DNS).
But their server might have their own limitations in terms of performance as well as caching.
When you search for something or access websites, things are mostly Google dominated. So Google’s cache is updated and fresh.
So when your browsing and internet usage is picked up from Google’s cache, your internet will be much faster compared to browsing using your ISP’s DNS.
If you are using Windows 10, watch this video to know how you can change your DNS to Google’s Public DNS.