How do I learn about hosting my catalog within Coupa?
You need to talk to your customer about how they would like to access your catalog.
How do I implement a cXML/punchout on my website?
You'll need a dedicated cXML developer or a third-party consultant, for example, Punchout2Go, to make your website cXML compliant. Once your site is cXML ready, provide your credentials to your customer. They'll handle the rest. For more information, see http://cxml.org.