Hi Angelica

Yes, you've got it - your domain name is your HTTP address on the web. I'd recommend getting a domain name that reflects your business name, exactly if possible. So if your company name is XYZ Virtual Assistants then you might want to purchase
www.xyzvirtualassistants.com [assuming it's not already in use by someone else].
And then you'll need to be aware that you must renew your ownership of your domain name each year, usually for the same cost at which you purchased it initially [about $10 a year].
I hope that helps