Q: Safari cannot open page because server cannot be found

I'm having problems on Macbook Pro with Yosemite. Most, if not all webpages cannot be opened in safari because the "server cannot be found." I've tried to troubleshoot a few different ways by googling the issue.

1. Tried running diagnostics, no issues found and no solutions offered
2. Tried monitoring connection while attempting to browse web, no issues detected
3. Reset computer
4. Reset router
5. Turned WiFi on/off
6. Cleared browsing data, history etc.
7. Tried using Chrome, doesn't work either

I've read that this could be a DNS issue, don't fully understand what that means. One solution offered is to "reset network settings" but I can't find where to do that on my Mac. Another option is to "delete current DNS servers" but I am not able to click them in the advanced network settings window. Any other ideas?

Thank you!