Add hosting partially and uploaded image path

I am brand new with Dreamhost, and hope someone can help me with this two issues. Many thanks in advance.

I have a domain in which I have created a record CNAME to redirect it to Bigcartel where I have my online shop. Then I do not have the “” fully hosted, just DNS.
Now I want to add some extra images to the shop in some additional pages I have created and I can´t.

The first issue is, once I have redirect my domain to Bigcartel (actually just the “www” part of it), I would like to add hosted the “” to Dreamhost and I do not know how.

The second one, is, once I have “” hosted, I know how to use the WebFTP from the main panel and upload the image, but which is the path of it, so I can copy in the css of the Bigcartel platform?
Is it possible just to copy that path and it will be visible in the web shop?