subdomains etc

[DarrylPurpose]

I have a doman - it's my name, DarrylPurpose.com. BUT this domain has my entire site, I DO NOT want to use it as a domain for my shopify store. I assume I can use something like this -- store.darrylpurpose.com, but I'm not sure whether I own this, simply because I own darrylpurpose.com. I also don't know if it's possible to use a subdomain (is that what it's called) like store.darrylpurpose.com for my shopify store.