As Wikipedia explains,
The Domain Name System (DNS) is a hierarchical distributed naming system for computers, services, or any resource connected to the Internet or a private network. It associates various information with domain names assigned to each of the participating entities. Most prominently, it translates easily memorised domain names to the numerical IP addresses needed for the purpose of locating computer services and devices worldwide. By providing a worldwide, distributed keyword-based redirection service, the Domain Name System is an essential component of the functionality of the Internet.
Google’s Public DNS will speedup your computer internet connections performance with faster speed for domain name lookup.
It is highest quality tool for any web developer, designer, IT engineer or even a common internet user who uses his internet on daily basis.
It will provide security & speed through greater browsing performance.
Navigate to below URL:
Now Copy Google Public DNS Server IP Addresses give on the page & paste it your current network settings as per below steps,
Go to: System Preferences in Dock > Network > Wi-Fi / Ethernet (Which ever is your current Internet network) > Advanced… > DNS > Add your copied DNS server IP addresses copied from Google Public DNS page > Press OK & Then Apply & you are done
It will look something like this,
Hope it helps,
Thanks & Regards