As mentioned, you should register your site with Google Search Console (GSC):
You should insure your site has permitted indexing (this is “on” by default in discourse). Check this setting to make sure:
allow index in robots txt
You should install this discourse plugin (works well, no errors in sitemaps at all)
After that, of course, you should create great unique content, but I understood from reading your your originally question, you asked:
How do we get Google to reference our Discourse site?
By “reference” we normally call this “index” and to index you must insure indexing is “on” and you should have a good site map (see above) and of course, a GSC account to keep an eye on things.
Content, is a different subject.