If you want to use it right away you may want to purchase your hosting with one of the hosts like mine, Dreamhost, that provides one domain free with hosting. ($9.95 for additional domains)

This is to "register" your domain. You spoke of "buying" a domain. While there are many domain names available at a premium it is very unlikely that you would gain any real advantage over a name you could come up with that is unused. Companies that provide registration and hosting have search programs to help you check out names to see if they are still unused and are free to use.

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Good Success!

Douglas County Master Gardeners
"We don't always get what we want, but we always get what we expect."