You need a domain name. This is the name of your website, and it usually ends in ".com" or ".net" Example: adirondackpc.com
There is a small fee for ownership of the name. The company I go through for domain names charges only $7 - $9 per year.

When someone visits your website, a computer somewhere (called a server) needs to electronically send them the information that will be displayed on their screen. This is called "hosting" and there is a separate charge for this service, but again it is a small fee. Plans start at $3 per month.

Most importantly, someone needs to design a site for you or you won't have anything to show off! I have completed websites for as little as $150 in the past.