Talking to newbies here... Domain names are text names given to I.P. (internet protocol) addresses. In other words, it's basically your address location on the internet.
e.g. www.239Creative.com - my personal website
Often times people may refer to a domain name as a web site name. Domain names can be .com, .org, .net, and so on. This is typically the first thing that you would "secure" when you are ready to get a web site.
When you acquire a domain name you typically are not buying the name, rather leasing the name since domain names require to be renewed. Some Domain Name Registrars offer one, two, three, five, and up to ten year plans.
Domain Name Tip #1:
When searching for a domain name try to capture a .com domain name. The reason is simply that .com domain names are the most recognized and easiest to remember. I would say .net would be the second choice.
Domain Name Tip #2:
Try to find a domain name that has the best and most keywords (while keeping it short) as part of the domain name. Let's say you are a water filter company looking for a domain name. Well, waterfilter.com is probably already taken. Maybe add some keywords to see what domain names are available like, cleanwaterfilter.com, healthy-water-filter.com, allhomewaterfilters.com, and so on. Search engines love domain names that are rich in keywords - matching content in the domain name and what you post on the website.
Hope this helps.