Port 8091 is Couchbase Server, not the Sync Gateway.
"Connection refused" implies the gateway isn't running. (Tech support: "Is your computer turned on?" :)
Also, even after you start the gateway I think that request will be rejected (with a 400) because it's not declared as JSON. You'll need to add a "Content-Type: application/json" header. This gets somewhat awkward with curl; I much prefer httpie, which lets me write that as
http PUT :4985/beer-sample/_user/jens name=jens email=
je...@someemail.com password=1234
(But if you stick with curl, it also lets you omit the "
http://127.0.0.1" prefix of the URL. Saves a lot of typing in the long run!)
(Also, you can skip the "name=jens" part because the name's already specified in the URL.)
—Jens
PS: If something in the docs led you astray, please let us know where the problematic part is so we can clarify or fix it. Thanks!