It sounds like you registered a domain, the charge for that might be 11.95 if it was a .com .net or .org, or it might be more depending on the tld. That buys you the domain for a year whether at dreamhost or somewhere else.
If you used a promo code or got one of dreamhosts standard promo's the first year is so cheap that it doesn't even make sense to pay monthly. I don't know the details of current promos but be careful here because paying monthly is MUCH more expensive than the annual plan. The rate goes up monthly and there is a "setup fee" that is waived for annual plans.