If you use Blogger, you'll have to buy a domain and have it redirected to your blogger site.
If you use Wordpress, you can do the same or you can install wordpress on a host and you wouldn't have to do any redirecting.
I had used eNom.com to register mine, but you can do it through your host company if you want to go that route. My hosting company let's you register a domain name for free when you have your hosting with them. It's 6.95/month US for 2yr contract. You get tons of space and bandwidth, in the TB (more than GB).
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