Domain names are a human-friendly version of IP addresses. The resolve process is a lookup between a name and an IP. For example, the IP address 188.8.131.52 resolves to www.google.com, and the domain name is far easier to remember than that long number.
On some Linux distributions, domain name resolving does not work out the box. Typically this is because a package isn't installed or a setup item wasn't completed properly. You may encounter errors such as:
Err:1 http://gb.archive.ubuntu.com/ubuntu xenial/main amd64 postfix amd64 3.1.0-3 Temporary failure resolving 'gb.archive.ubuntu.com'
The fix is quite easy. All you need to do is edit a file and add in two lines which tell the networking system where to go to look up domain names.
sudo pico /etc/resolv.conf
If this file is empty then this is your problem. Simply add the following lines to the file, save and try to access the domain name again.
nameserver 184.108.40.206 nameserver 220.127.116.11
Now you should be in business.