Your Mac uses DNS to be able to connect to any internet domain address – like http://becomethesolution.com. Basically, without DNS you would never be able to type a web address name into your web browser and have it resolve. You never need to worry about managing your DNS because your ISP (Internet Service Provider) (such as AT&T or Comcast) automatically pushes their DNS to your home router. Thus, all computers connecting to your router use the same DNS servers.
When you purchase Internet from an ISP, you are essentially paying to use their DNS servers. There are many public and private DNS servers you can use. Some private DNS servers promise 100% uptime but come with a price.
What should I do when my Internet is down?