At present, mom provides no mechanism for automatically generating cover pages. It's a situation not likely to change, given that what's needed on document covers changes from document to document, both in terms of style and content. And, more often than not, what goes on covers is matter of personal taste.
If you want a document to begin with a cover page, typeset the cover (using the typesetting macros). At the end, invoke NEWPAGE, then set up your document in full (see Tutorial -- Setting up a mom document), invoking START as usual once you're done. The cover page (and any typesetting commands on it) will have no effect on mom's processing of the document itself, the first page of which, moreover, will be numbered "1" unless you instruct her otherwise with PAGENUMBER.