Every computer, or device, connected on a network is assigned a unique identifying number, called an IP address (like 198.120.1.14). This serves the same purpose as a physical address in real life and allows other computers on the network to send and receive information from that computer.
When we want to visit a website we typically don't use its numerical IP address as that would be quite difficult to remember. Instead, we use its domain name (like some website.com). Computers, however, don't understand this language (but binary) and so they look for an IP address that matches that domain name.
This search starts with the recursive resolver, which is usually operated by your Internet Service Provider (ISP). This server answers the question "what is the IP address for this domain?".
Next, the recursive resolver asks the root server for DNS information on top-level domains (TLD) like .com.
The root server then sends it to a TLD name server, which keeps the IP address info for 2nd level domains within the TLD. The TLD server tells you what the IP address for the domain name server (DNS) is.
Finally, the recursive resolver goes to the DNS server to ask for the IP, which the DNS returns, and your browser retrieves the website you wanted to visit with that IP address.