Hosting a domain I don't own

I am curious. Can I host a domain on my account that I don’t own? My SIL is looking to get started with a site but I would be the one managing it for a while. If it is possible, how would I set it up?

Sure. Just add the domain to your dreamhost account. Then whoever owns the domain logs into the account at their domain registrar and sets the nameservers for the domain to,, Then wait for the DNS magic to happen (depending on lots of factors, then DNS wait might be anything from a few minutes to 24 hours).