http://docs.shopify.com/manual/settings/domains/outside-provider

https://docs.shopify.com/manual/settings/domains/third-party-domains/popular-providers/dreamhost

 DNS Settings:

DOMAIN	CONFIGURATION
TWO LEVELS (E.G. MYWEBSITE.COM)	point A-record (IP address) to 204.93.213.45
THREE OR MORE LEVELS (E.G. WWW.MYWEBSITE.COM OR BLOG.MYWEBSITE.COM)	CName “www.YourStoreName.com”

“www.YourStoreName.com” is the name of your shopify store, you get this from their side.

 On the Dreamhost Side:

Go to your  Manage Domains Page  and make sure the domain is DNS only. If you have hosting on the domain, use the “remove” button under the “web hosting” column:

Once the domain is dns only, click the dns link under your domain name and add these records:

Custom DNS Options:

Name: subdomain, leave blank for naked/root domain

Type:  type of dns record, such as A record, Cname, TXT

Value: Target

Settings Needed for this setup:

Name:  leave blank for naked/root domain

Type:  A

Value: 204.93.213.45

---

Name: www

Type:   CName

Value:  www.YourStoreName.com 

Note: This guide has been created to help simplify setting your domain up. The service you are pointing your domain to, DNS can/might has changed. Always check the hosts official page to verify the records.