A domain name is the characters you type in the URL bar to go to a website(ex: www.google.com).Â Without a domain name, it is still possible to access a website by using its IP address, which is something like 126.96.36.199(an IPv6 IP address is longer). It is a lot easier to remember a domain name than it is to remember an IP address. Anyone can get a domain, but they generally cost money. When you go to a domain, your computer sends a request to a DNS server, which then tells your computer which IP address to go to(read more here).
If you are looking to get a domain name, I highly recommend Google Domains, which costs only $12 a year, and includes a privacy option, which hides your address,phone number, and email from a WHOIS lookup.